Yep, like I said, I'm sure many people haven't heard of it, probably more than have heard of it. But your comment actually supports my point. How many other musicals have you heard about on John Oliver?
"Hamilton" has reached the point where it's a part of the mainstream pop culture, discussed on national morning shows, late night talk shows, etc. That's unusual for a Broadway show, these days.
I had only heard about it from watching John Oliver.