How come most relationships in Marvel and DC don't last long?

And then this week, it all went to hell. Creative team J.H. Williams and W. Haden Blackman announced they'll be leaving Batwoman, citing DC's editorial interference and the company's total refusal to allow characters Kate Kane and her girlfriend Gotham City police officer Maggie Sawyer, to marry each other.Earlier this year, Batwoman proposed to Maggie twice, and the fact that DC didn't make a big public thing about it should have been a warning sign that they were never going to go through with it. "We were told emphatically no marriage can result," said J.H. Williams via Twitter. Although he felt that the idea "was never put to us as being anti-gay marriage" it just seems DC doesn't want any of their heroes - be it Superman and Lois, or the Flash and Iris - to be married. Because marriage is for old people, and we all know no-one over thirty reads comic books.