Well some of it is the mask. If you have say an eight hour flight and you have to account for at least 90 mins in the airport at one end and 30 at the other, you are wearing a mask for 10 hours and that doesn't feel great.
Then the airports seem more frazzled - there are people not wearing masks and coughing and that gets everyone tense, and sometimes the security people intervene and sometimes they don't.
Then in flight there seems to have been some edict that food service is a problem - so it has all been stripped down to basic - no relaxing with a glass of wine.
Admittedly this is US airlines and probably a bunch of it is cost cutting measures which I understand. But it adds up to not such a great experience.
My second trip (February) was meaningfully less grim than my first trip - so it may be that things are improving.