Tail calls make stack traces harder to read and it looks from the outside like java development is primarily about reading stack traces

The strange thing is that the JVM can handle them because Scala and Kotlin have them. Java though, doesn't.

Scala and Kotlin just implement them using a trampoline, the JVM does not itself support tail calls.

How do they do that? I thought it would need to be done at the JVM level so that stack didn't grow.

Every recursion can be converted to code that uses only a single stack. Tail calls can be easily eliminated at compile time automatically as well, that’s why it only needs compile-time support — I don’t specifically know what Scala/etc do, but the mentioned trampoline is basically just a function pointer one can jump to, accumulating results in some non-stack data structure if needed.