As a millennial who is now the same age as Al, I get it a lot more. When you are 40, come home from a job you hate that doesn’t pay enough, and are physically and mentally exhausted, yeah, sex isn’t as appealing, even if married to Katey Sagal. You just want to plop down on the couch, turn off your brain, and be left alone. Peggy being horny is just a reminder that his wife refuses to work (neither outside nor inside the home) and has more energy.

But also remember they originally offered the role to Rosanne Barr, which would have been even more understandable.

Al Bundy spends all day working on his hands and knees for women only to come home to more demands from a woman he’s not emotionally attracted to.

It’s supposed to be ironic that he can’t derive joy from the one bright spot in his life, a sexy wife who’s DTF.

Not everyone has, or keeps their desire for sexual activity

The whole show is peek boomer "haha wife bad/annoying" humour.