In short, he was too fat

It was at the conclusion of one of these promenades that he had asked her to be his wife, and she had replied that the only obstacle standing in the way of the suggested merger was his adipose deposit. She refused, she said, to walk up the aisle with a human hippopotamus.

Horace Prosser chuckled again. "The whimsical way she put it was that a woman who married a man my size ran a serious risk o being arrested for bigamy. She confessed that she had often yearned for someone like me, but was opposed to the idea of getting twice as much as she had yearned for. Very bright, amusing woman. She comes from Pittsburgh."

(from "The Fat of the Land," by Sir Pelham Wodehouse)