It's actually more rare for people to talk down on blues or slower playing. It's way more common for some guitarists to talk down on shredding or "noodling."
I think the simple reason is: these people can't do it! So instead of admitting that they just can't do it, they try to find a reason why they DON'T WANT to do it so they won't have to admit they just can't.
Because looking back, just about every person I can think of who talked down on fast playing or sweep picking couldn't do either. I think I'm on to something here...