Writing a low latency garbage collector (with decent throughput) is a non-trivial engineering problem and requires both high calibre engineers with specialized skills and a lot of funding. I fear the time lisp community has had either are long gone.

How much did the development of Azul's C4 or Oracle's Shenandoah cost in terms of money, talent and time and how much has this work lowered the barrier for less well resourced languages? I don't get the impression that the answer to this question is: "enough that we will soon see low-latency, high-throughput garbage collectors becoming the norm".

Some older VMs like Erlang's also do very well in avoiding GC pauses.

In Erlang's, the key is that garbage collection is per process. (Note that Erlang processes are analogous to Golang green threads, not OS prcessses.)