Why does Kugelmass marry Daphne in The Kugelmass Episode?

The most important thing to understand about the character
of Kugelmass is that he is a fundamentally shallow and self-centered person. We can
infer that he married Daphne because, at some earlier time, she was relatively
attractive and had money. Speaking with his therapist, Kugelmass reflects that "Daphne
had promise," but that she subsequently "let herself go" and swelled up "like a beach
ball." She also had some money, which had to be attractive to a man who was "up to his
neck in alimony and child support."

Kugelmass evaluates all
of his relationships from the standpoint of personal gain and satisfaction. He wishes to
have an affair because his current wife, Daphne, is an "oaf" and no longer attractive.
Even when he embarks on his torrid affair with the fictional Emma Bovary, he seeks to
get rid of her when the relationship becomes too inconvenient and personally taxing. He
is not introspective at all, and constantly searches for external solutions to his own
unhappiness and dissatisfaction. Presumably, there was a time before the "present" of
the story when he saw Daphne as the solution to his problems. Kugelmass never sees any
need to change himself, only to find people who can accomodate his non-negotiable needs.
Perhaps this is why the therapist at the beginning of the story tells him that his
problems "run much deeper" than an affair can solve.