That's why Phyllis Diller had to tone down her looks. There's a great story that came out about her a few years back and how she had to purposefully make herself unattractive. Traditional female beauty as defined within patriarchy objectifies the beautiful woman, thereby rendering her subjective humor absurd or terrifying or both.
There are plenty of brilliantly witty women who are "beautiful" by traditional standards, but only recently has that become conceivably tolerated. Who was it who said that women fear men will kill them, and men fear that women will ridicule them?
The male approval one gets with "beauty" is fleeting, and every "beautiful" woman knows that. Humor isn't about knocking one's self out. It's an outlook that congenitally funny people feel compelled to share because that's the way they see the world. "Beautiful" women are just discouraged socially over and over and over again from being witty--they're usually punished for it.