VMAs sound expensive. Of course a 64 bit counter is going to work for moderately expensive things.

If you have a multithreaded app doing a lot of communication, that's going to be a lot of cheap allocations happening very fast.

Reducing GC and allocation overhead results in more allocations being done, and pushback against ever-expanding allocation behavior is more of a challenge. Instead of ten other things being a higher priority than judicious data architecture, it's dozens or more.