I think one of the issues people have with the old comedies is like anything, they remember the good stuff, they don't remember the terrible rubbish, or the flops.
For every blackadder, Faulty Towers or Young Ones there were dozens or hundreds of immediately forgettable series, even the classics had their dud moments (IIRC first season of Black Adder wasn't anything like as good as season 2 onwards where they got their feet).
There is also an element of what one generation considers funny another often doesn't due to changes in shared experiences, I remember when the "in" jokes for popular stand-up TV comedy was very heavily focused on "ooh my my mother in law is awful" and "my wife can't cook".
Some of those shared experiences might have been long term (Carry on Sergeant etc played a lot on people's experiences in the military/with military films), some might have been quite fleeting and relied on things like you being around for a particular event or time period, whilst others about things that happened long enough back that you forgot the bad for example Dad's Army was long enough after the war to dull the bad memories, but played on the sort of people everyone knew from the time.
These days there is probably more comedy available on TV than ever before, and as you'd pretty much expect the highest profile stuff is largely the blandest/widest appeal because that's what gets the viewers thus the good time slots and the press - I can't stand Mrs Brown's Boys (it feels like some third rate comedy from the 70's) but it's popular, I could never understand the appeal of Friend, but I loved Black Adder, classic Red Dwarf, I can still chuckle over Last of the Summer Wine (although the Russ Abbott era was terrible), I can enjoy Steptoe and Son, the Carry on Films, etc et, I can and do enjoy "edgy" comedy but there are certain types of "comedy" that just make me change channel.
My brother referred to a couple of American sit coms as "frownadies" because as he put it, he ended up less amused at the end of an episode than he was going in (I think he was referring to one that was basically 4 extremely obnoxious characters with no saving graces where every "joke" was a very tired stereotype that mocked a minority group and had no effort put into it, yet apparently it's popular in the US).