I don't think it's unreasonable to say the status of missiles in Star Wars is a bit weird.
In lore, they're all over the place- they're considered an important part of a competent starfighter design, and are loaded in magazines as though they're expected to be expended in large numbers. All the Rebel starfighters I can think of either do carry or can carry them, and numerous examples of starfighters from other factions do as well. They are often described as being interchangeable with Proton Torpedoes, so craft which can fire one can fire the other. They're quite common as a secondary weapon in Star Wars games too. Elite starfighters which don't carry torpedoes often carry seeking missiles for use against other fighters instead. And yet, we never see them used that frequently in the movies.
In the movies, missiles are treated as special weapons and employed sparingly as such. Instead, laser cannons are by far the preferred weapons for ship-to-ship combat.
This feels intuitively weird from an audience perspective. First of all, the implication between the lore and the series is that, essentially, everybody has missiles but nobody uses them, which begs the question if nobody uses missiles regularly why do so many craft carry them? Second, we know from our own universe that air-to-air missiles essentially rendered fighter guns obsolescent (Yes, it's a bit more complicated than that- I'm generalizing), which begs the question why haven't they done the same for the Star Wars universe? In short, what we're told and what we're shown feel contradictory.
There is an explanation put forward, though I'm unsure whether it's canon or fanon, that would partially explain this discrepancy- which is that Star Wars battlefields are so saturated with EW that in a close dogfight missiles are essentially useless. It certainly seems to be the direction some official materials have gone- like the Squadrons short "Hunted", where the TIE Interceptor pilot's response to having a missile fired at him by an X-wing, is to annoyedly turn his EW on, and the missile immediately curves back around towards the X-wing that launched it. However, this doesn't explain why Star Wars ships still carry missiles if they're so easily countered by even a lone fighter.
I think there may be a doctrinal explanation which has been missed.
See, while the lore and screen may be inconsistent on the frequency of missile use, the screen itself is remarkably consistent on how missiles are used. While I can't be sure I've seen all examples of on-screen missile use by starfighters in canon, a good 80% seem to go like this:
Launching starfighter gets behind target starfighter
Rather than continue firing laser cannons at target starfighter (for which it is still within range), launching starfighter fires a missile instead
Missile streaks out of launcher, quickly closing the first half of the distance to target
As missile approaches target its overtake speed drops considerably, eventually just barely gaining on the target starfighter
Target starfighter Does Something, but generally does not out-maneuver the missile
Missile fails to hit target due to target starfighter's actions
While I suppose it is possible that in all such cases of avoiding the missile an exceptional pilot is involved, the broad theme seems to be that firing a missile against a fleeing target in a tail-chase (an optimal position for guns) is not ideal (an exception to this seems to be the Tri-Fighter's discord missiles, which we see disabling a jedi starfighter with a rear-aspect chase shot twice). That said, it also seems to imply that, while it may take a while for a pursuing missile to catch a target, hard maneuvers by the target will fail to shake the missile. If this is well known in-universe, it might explain why we so rarely see missiles used in dogfights by starfighters. Essentially, every missile launched from a tailing position instead of continuing to fire with laser cannons is a gamble- maybe you'll hit him, but only if his EW isn't working or he's literally asleep at the stick. If it hits, it'll save you the effort of getting a guns solution, but if it doesn't no additional amount of missiles will hit either. In a dogfight, chances are neither of those is true, so guns it is. In a long chase, it may be worth the attempt That still doesn't answer the "Then why bother?" question, however.
I do think there's an explanation there too, but it's a bit more tenuous. There are two contexts where we see missiles being used regularly and effectively in Star Wars. The first is ground strike- although they aren't starfighters, the LAAT gunships' missile launchers appear to function similarly to starfighter missile launchers, and we see them using their missiles extensively during 1st Geonosis against ground targets. Additionally, we also see missiles used with consistent success both as surface-to-surface weapons by Juggernauts and Hailfire droids, and as surface-to-air weapons by handheld rocket launchers. Thus, it's possible that starfighter missiles are actually there for air-to-ground rather than air-to-air. That said, if we discount LAATs to my knowledge we don't actually see starfighters doing this.
Another strong possibility is a lot more tenuous, because it relies on the 2003 Clone Wars series, which is both no longer canon and heavily stylized. However, it is the one place I can think of where starfighters use their missiles regularly and en mass on screen. Specifically, in season 1, during the space battle over Muunilinst, a formation of V-19s succeeds in destroying a large formation of droid-piloted Geonosian starfighters with a surprise volley of missiles ordered by Anakin. Anakin himself uses missiles from his starfighter to destroy another formation of droid fighters in a rolling head-on attack, though his fighter fires about 50 missiles in that scene, so it's deeply questionable how much stock should be put in it.
What this does seem to indicate is that fighter missiles in Star Wars are weapons best used from ambush. An enemy which sees the missile launched usually has time to run from the missile long enough to negate it with EW or do something else. An enemy which doesn't see the missile launched or without enough time to take action will almost certainly be hit and destroyed by it.
These requirements for effective employment mean that in order to be used effectively, missiles should be launched head-on against an unsuspecting target. We don't see this engagement scenario on-screen very often (mostly because, if you're engaging a target head-on, they probably see you coming), thus we also wouldn't see missiles used effectively on-screen very often. Another way to look at this is that Star Wars missiles are a 90/10 weapon. 90% of the time they're ineffective; 10% of the time they're spectacularly effective. Thus, though a starfighter doesn't need missiles to be effective, anybody relying on their starfighters usually buys them equipped with missiles.
Is this at all convincing speculation? Or am I waffling to no purpose?