The Destruction of the Death Stars and Star Killer Base ensure the Jedi will never return
So consider this. The Jedi build their lightsabers out of Kyber Crystals, extremely rare semi-sentient crystals found primarily on Ilum, Jedha, and and a handful of other worlds. Getting them was a pilgrimage and rite of passage.
The Empire powered both Death Stars primarily by Kyber Krystals, including their planet killing super laser. As usual, the Emperor liked to make a mockery of the Jedi, using their primary tool of defense and Justice into his intrument of Tyranny. To do this he strip-mined all of these world's to a ridiculous extent, essentially destroying many of them. Ilum, the most Kyber rich and sacred of them was cored out to become a weapon itself, as Star Killer base.
And while the rebellion's success hinged on destroying all three of these terror weapons, it also meant destroying the majority of the known Kyber Crystals in the galaxy.
Surely it was not all of them, but it would make any restoration of the Jedi Order a shadow of it's former glory, as lightsabers would be difficult to construct, due to lack of materials.
The Empire ensured the death of the Jedi, not only in Order 66, but by using all their Kyber to power super weapons.