People chanting “If everyone just did X, Y wouldn’t be a problem!” without seriously addressing why everyone doesn’t just do X already, or making a serious proposal for how everyone is going to just do X from now on.
A phenomenon not limited to dieting.
I don't know people who just give the "trite" advice without any actual consideration of the difficulty.
I do see a lot of people ITT who were accused of doing so but who aren't actually doing so.
And I've known quite a few people who get really annoyed at constantly having to hear about how impossible it is to do things that they've personally actually done.
Yep. When 1 or 10 or 100 people do a thing, it's a "them" issue. When 100,000,000+ do a thing - it's a wider issue, and asking those 100,000,000 to do it differently just isn't a useful strategy.