Tis an obvious cheap shot.. like the mother-in-law jokes.. Men and women comedians do the jokes about husband and wife thing.. Interestingly many comedians would say they adore their wife, but the wife jokes are easy and to some extent expected. An easy laugh.
In fact in my earlier day almost all the comedy was men being sexist about women or making wife/mother-in-law jokes, oh and racist jokes too -easy laugh and people fell into that trap.. Now audiences and comedians tend to be more sophisticated.
If they truly are perhaps is because so many people are married. Just like comedians do a lot of jokes about anything that is common to lots of people because they figure they will relate. I don't know but I never thought jokes that only disparage and belittle were very funny. Like Joan Rivers who for most of her life though I guess she was very popular just seemed depressing. Until she started wisecracking on that fashion show on TV at the end of her life. Maybe to me wisecracks are funny and disparaging is not. You can make fun of without disparaging. Bill Cosby and Richard Pryor, also George Carlin I thought were very funny. So was Ellen DeGeneres when she did stand-up and I've seen on TV a lot of people I guess not very famous who I thought were good and I remember.
Situation comedies on TV degenerated into just cracks about wives spending their husbands money and husbands not lasting long enough and I stopped watching all of them. To me those are serious issues. Just like marriage to me is serious. I always wanted to marry but did not until I was 53 and I take it seriously as does my husband. Though some people on here think not seriously enough. I don't know - let people laugh at what they find funny. I like to laugh too but on the whole I guess you could say that neither I not husband are what you might call "fun people". Too much to be earnest about, too much to do. And oh I would never order my husband around like in the cartoon. We respect one another and enjoy being together. Of course we have our differences as well.
A successful comedian has to consider the audience and tell jokes that that audience can relate to. I can't think of a culture that doesn't get involved in marriage, so "it's a topic that all audiences understand."