When I'm too lazy to get off the couch to change the channel, some perspective is good.
When work sucks, or the education I'm putting myself in debt for sucks, or when I get sick, perspective is stupid. What I have here is bad, and fixing it would be good. And the idea of complacency espoused in the "Be grateful for what you have" through some of it is entirely counterproductive. If I'm unhappy about work, being pissed off about it is my first step to talking to the boss or changing job. If I'm unhappy with my education, that's the first step to organising a student body complaint to the school. If I'm sick, yes things could be worse. But it's still bad. It can always be worse.
So FWP is funny, but the demarcation between what's a serious problem and what's pointless whining about irrelevant bullshit is ignored by some.
And if I've got the flu and a migraine, if you remind me that I could be a quadraplegic eating mosquitos, I'm going to flatten you when I get better. And then tell you it could be worse.