u/Maleficent_Sound8587

Most sand is predominantly made from Silicon Dioxide (Quartz). Coastal sand specifically is mixed in with ground up and eroded sea shells in the form of calcium carbonate, chemically similar or identical to bone structures. The two crafting recipes attached show different ways renewable sand could be implemented, with one way using a 2x2 grid to get one sand block and the other way using a 3x3 grid to get 4 sand blocks.

The 3x3 crafting recipe can also be used for red sand. This makes both items easily accessible as sand is either cumbersome to get or nigh impossible / implausible depending on your situation.

Superflat play throughs requires lucking out on a wandering trader and potentially duping it as a reasonable source and although this is a bit more of a niche, but sand can be difficult to obtain on Java with world gen mods that enhance biome size and world generation.

And this is ignoring the existence of SMPs where depending on the size of the server and the time and energy you yourself have depends on how much sand is available, as it can become sparse quite quickly within a local area, leading to terrain deformations and exploring 10s of thousands of blocks laterally.