I once heard Dr Ruth on TV say something about how sex can be hotter when it has a sense of being forbidden. That in some way, as it becomes more open and accepted, it also has the danger of becoming less exciting.
Comedy can be a wonderful vehicle to bring issues into awareness. In the process, at first what might be very funny, might later turn run of the mill and maybe even beyond that dull or after that it could turn into a turn off. Some things will always be funny. So to listen to those fat jokes, most of that was just stupid by today's level of consciousness. Some of it still funny. Being pushed through the Holland Tunnel to clean it will probably always maintain its cartoony affect upon the mind. So that will stay funny. Whereas other past humor can become in bad taste as we lose our taste for it.
Modern example: that crass bitch Campanelli? Hold on. Google: Lampanelli. I think her humor is disgusting. It might have been funny when Don Rickles was doing it 40 years ago (and I didn't even think he was real funny) but today? With today's awareness? Yikes. She's a bitch, making money by insulting people. My brother and SIL went to see her recently, all excited to go but they reported afterwards that they didn't enjoy the show at all. Maybe one out of 10 lines of hers is funny. Maybe even very funny. But the rest is crap.
That Diller (who I loved) had a whole routine on fatness in the 70s is kind of interesting because we didn't have the obesity then that you see today. But that is when people started fattening. So that humor might have been a prescient response, as a good comedian, and she certainly was one, tend to be able to tune right into society.
I recall my mom always kept a great figure, hopped up on "diet pills" in the 60s (it was fucking speed we later learned) and by the 70s she was into her exercises and protein shakes way before that was a trend, so I grew up with this stuff. So in the past when there was not a lot of obesity, the joke might have been more of a matter of breaking the ice whereas today it might be more a case of breaking the rules, of breaking out rude.
Sometimes being overly sensitive is neurotic. Sometimes our sensitivities are just.