Fat discrimination may be one element here, but not the only one.
As GordoNegro wrote, airlines are increasingly willing to push passengers off planes as soon as only minor complaints occur to make sure all is quiet on board.
The second issue is the belly/midriff baring one. This remains off limits for females - above the age of maybe elementary school, no matter what size, ethnicity, etc. - in many situations and is immediately sanctioned.
Social media are full off "models", "influencers", etc. from all walks of life complaining about being denied access to all sorts of venues/events/institutions for showing up with a bare midriff.
That said, in the last years, pressure on men has also mounted, not to appear in many places shirtless - again looking into omnipresent web evidence.