I try and read and respond to as many comments as possible because I agree with you - and I think there's plenty of action to be found over in the comments section. As my work as become more popular it's become harder and harder to reply to every comment - but I'll try and engage with most.
I guess the more successful you become as a blogger the more of a burden it becomes to reply to everything. Luckily I'm not there yet - but I Imagine there must be a breaking point past which you never get any writing done. I'd love for Medium to monetise comments too - that'd be ace.
Great article - I'm with you on this one. Comments rock! :o)