Wow, I was assuming there was a way to do it that I wasn't seeing, not that this is intentional! I'm also struggling to understand how they are thinking that people use sug-tags. Anyway, thanks for the suggested solutions! The filter without subtags is definitely a candidate, but why can't there be a keyboard shortcut for it too?
I'm also thinking that I could turn my existing main tags into sub-tags, and then adding a more general main tag that I won't actually click on. (Sort of like a navigation menu where you can't click on the button itself.) But that is a pretty major work-around so I'll have to think about it first.