It comes from a desire to run in the exact opposite direction as the JVM, which has options for every conceivable parameter. Go has gone through a lot of effort to keep the number of configurable GC parameters to 1.
At least with code hacking around the GC's behavior that code ends up being portable across the ecosystem.
There doesn't seem to really be a good option here either way. This amount of tuning-by-brute-force (either by knobs or by code re-writes) seems to just be the cost of using a GC.