https://bugs.java.com/bugdatabase/view_bug?bug_id=4726340

but that looks like a dead link and no wayback archive..

IIRC, basically it's because some parts of the JVM use stack unwinding to figure out what userland code is calling certain system code.. also the current stack frame has metadata about lock status used for allowing re-entrant locks that you lose if you elide the entire recursive call (which the initial proposal did by only removing the few bytecode instructions that set up the callstack frame and return from it).

A more informal proposal from ~2016 allows for soft tail calls and hard (annotated) tail calls, with some restrictions that evidently avoid issues with system calls and lock/reentry maintenance:

https://web.archive.org/web/20161112163441/https://blogs.ora...

And a video by one of the JVM architects at Oracle about adding TCO for Scala

https://www.youtube.com/watch?v=2y5Pv4yN0b0&t=1h02m18s

Also previously featured here on HN, a way to do it that avoids security concerns, by using goto instead of strictly deleting bytecode instructions:

https://news.ycombinator.com/item?id=22945725