>The problem is that writing genuinely performant Java code requires that you drop most if not all of the niceties of writing Java. At that point, why write Java at all?

The reason is quite well known. Supporting multiple languages is a cost. If you only have to support one language, everything is simpler and cheaper.

With Java, you can write elegant code these days, rely on ZGC, not really worry too much about GC and get excellent performance with quick development cycles for most of your use cases. Then with the same language and often in the same repo (monorepo is great) you can write smarter code for your hot path in a GC free manner and get phenomenal performance.

And you get that with only having one build system, one CI pipeline, one deployment system, some amazing profiling and monitoring tooling, a bunch of shared utility code that you don't have to duplicate, and a lot more benefits.

That's the reason to choose Java.

Of course, if you're truly into HFT space, then they'll be writing in C, C++ or on FPGAs.