In addition to the hundreds of blocks and mobs that would need to be implemented properly and rarely are, the lack of mod support is a killer.
The only "complete" reimplementation of Java Minecraft that I'm aware of is Bedrock.
The only "complete" reimplementation of Java Minecraft that I'm aware of is Bedrock.
For example, in Java version if you take a circuit and activate it with a button/lever - it would always behave in the same way. In bedrock same setup could have random result. And "random" is something you don't want in a large sophisticated contraption.
I'd guess it's caused by some race-conditions in bedrock implementation, but alas it wasn't fixed in 7 years.