We are in a Full-Frame Revolution, Who Needs APS-C?

I've written before about how APS-C cameras and other small sensors are more or less moot these days. The exceptions to that rule have to do with them being in compact cameras -- that's something we can get behind. But interchangeable lens small-sensor cameras aren't pushing any boundaries and are all pretty much the same things. So with a second-hand used camera market having such low prices these days, what's the point of going for smaller-frame cameras?