"are clearly their own worst enemy"
And there is the key. I'm unlikely to get a cyclist overtake me too closely at 40mph whilst on their mobile. And I've yet to see a cyclist negotiating traffic whilst reading a book. I've seen plenty of cyclists doing stupid things, but at most I've been inconvenienced (the young woman yakking on her mobile whilst riding the path through Whitworth Park - had to sit behind her at 8mph for the duration).
I've seen people point out stupid cycling on this forum before now, but speaking from my own perspective, I'm far more likely to notice and comment on crap driving because;
a) Drivers are more numerous

Drivers are far more dangerous to me if they are unable to drive safely around me.