I'd say on the contrary. They chose it even while knowing they'll gonna need to hack generics. (Same in k8s, generics hacked together in a few different ways)

You're starting from the assumption that the Google developers took a clear-eyed decision on the merits, which I don't share.

What do you suggest guided their decision?

It's quite likely that, being at Google, they were already familiar with Go, people around them were using it, and there was a comfort factor with it being a Google project.

It's rational to take these factors into account, but they don't reflect on the merits of the language itself, and aren't necessarily transferable to other people choosing programming languages.