It’s wholly a community effort and not supported by Jetbrains, which means it will always be at a disadvantage. Even development on it continues, it’ll always be a few steps behind the current version of Kotlin and will probably be missing a number of things compared to the autocomplete in Jetbrains IDEs.

It’s also built on the internal APIs of the Kotlin compiler, which are subject to change at any time. If Jetbrains shifts those around too dramatically it could break the LSP beyond the point that anybody is willing to repair it.

For corporate-developed languages first party LSPs are important.