Why OptiFine is banned in 1.15+ but still be allowed in 1.14-?

Optifine modifies many aspects of the game to be non-vanilla. In 1.15+, better mods which are faithful to vanilla are available (Sodium).

above response is wrong. its banned because its optifucking bad

Optifine basically modifies many ways the vanilla game operates and are not vanilla and mods like Sodium,Lithium,Starlight,LazyDFU,Krypton are much better you can also find them here https://www.minecraftspeedrunning.com/public-resources/mods