That's true for apps & devices, but generally I think they can assume that a human is doing the logging in for one of their websites. If they can't assure themselves that it's mostly true they have a serious issue.

There are plenty of passwords managers that will do an auto-login. Anyway, the last time I've logged into my Google account is months ago - I only access it on trusted devices with long-lived sessions, and I suspect this is the case for most users.