Google maps won't give you a route at all in public transit if you include multiple stops. I think generally, for public transit, you either have to use google maps to extensively look up and plan your own route, or you have to use a different app. There's one just called "transit", which I think people generally use, has good integration, and sometimes local agencies have their own app or will use a different one, there's a handful of generalized ones.

But yeah, in any case. Probably, Google should be better about that.