It isn’t just fat people who have a problem. I was sitting next to a guy with wide shoulders - he wasn’t fat; he could easily buckle the seat belt. But he was in a middle seat, and his shoulders were too wide for the seat. He was trying to sit sideways, so I took sympathy - not enough to give up my aisle seat, but enough to let him rub shoulders. :-)
That one really is the fault of the greedy evil capitalists at that Giant Corporation called Big Airline who decided to maximize their profit by making the seats 17 inches wide.
It’s not the broad shouldered guys fault.
Let’s sue the Airlines. Class action suit anyone? Some greedy trial lawyer out there has to be willing to take the case.