Until a few years ago, gccgo was well maintained and trailed the main Go compiler by 1 or 2 releases, depending on how the release schedules aligned. Having a second compiler was considered an important feature. Currently, the latest supported Go version is 1.18, but without Generics support. I don't know if it's a coincidence, but porting Generics to gccgo may have been a hurdle that broke the cadence.

Seems doubtful, given that generics and the gccgo compiler were both spearheaded by Ian Lance Taylor, it seems more likely to me that him leaving google would be a more likely suspect, but I don't track go.