No. Just no.
At the broadest, deepest level of zoom, every_game_ever_ is about fun.
I mean, yes, if your position is "degenerate forms of any play/game or people held against their will to play something or people who have an actual affliction but cannot stop playing something" means that the broadest, deepest level of zoom of those games cannot_be_about_fun.
Then sure.
But D&D 5e isn't excused from that. There can be dozens of degenerate, dysfunctional reasons for playing 5e that have nothing to do with fun. I can name hundreds of them the same way you can for Chess or Poker or Basketball.
I mean, just yesterday I went climbing for 1.5 hours exclusively as a technical training session. I didn't do it for fun. So I guess climbing, at the broadest level of zoom, isn't about fun.
Two days ago I played basketball in order to rehab a tweaked ankle and get used to the Florida heat and work on getting a specific brand of fitness up (which I can't get elsewhere). I didn't do it for fun. So I guess basketball, at the broadest level of zoom, isn't about fun.
Or someone doing a thing to escape a bad relationship/situation at home.
Or someone doing a thing (like poker) because they have an affliction.
There are so many examples of this. D&D 5e isn't exempt just because it says "have fun!" on page 3 of the PHB. I mean, the first time I ran it was an utter tutorial to work on my handling of the Social Interaction conflict mechanics and get a feeling for encounter budgeting/CR! It wasn't fun!