Honestly, I think it is because the Scala community was/is/can be so pedantic and bickering and often combative and toxic that it lost all momentum and appeal.
Nobody wants that culture in their workplace. Also the dysfunction is visible in the technical fragmentation of the ecosystem
Kotlin’s structured concurrency and coroutines as a library are remarkable pieces of software engineering. It’s a great language and ecosystem… but
Modern java has been grabbing features from all the “better Java” languages at such a pace that the big gap right now that I see is the question mark operator.
I wish it got more love.