There's a major historically-contingent component to this, too. The Island ECN, later absorbed into NASDAQ's ECN, originally ran its matching engine as one of these low-latency Java processes, writing everything using explicit object pools to avoid doing any GC on the critical path, as this was long before Zing was around.

This was a pretty reasonable choice at the time, as this was long before C++11 was around, and Java just offered a lot of advantages for developer ergonomics.

A natural consequence of this is that a number of HFT shops that were seeded by ex-ISLD devs just fell into using something like the ISLD tech stack, which at least at first involved a lot of GC-free Java.