For someone not well-versed in language implementation details, it may very well feel random.
I've been using Go as my primary language for a decade, and the lack of generics on methods was surprising to me the first time I ran into it, and the reasoning not obvious.
Yeah. I'm not claiming they didn't back themselves into a corner here.
There's no theoretical reason not to have it, the reason is because of a random intersection of other design decisions... unless you're saying they made those choices fully expecting to have these restrictions on generics later?
I've been using Go as my primary language for a decade, and the lack of generics on methods was surprising to me the first time I ran into it, and the reasoning not obvious.