minecraft has a file which modloaders edit to mod the game, update 1.21.1.3 made that file completely unpredictable so most developers gave up on trying and just joined the minecraft partner program. They would do this for java edition, but that would give them a terrible reputation. Why not develop your own client? The server APIs are open source.
mojang released the minecraft bedrock protocol docs, probably to stop retaliation against the removal of modloaders.