It wasn't just commercial. Back then, the characters were portrayed generally like kids in adult bodies. Heroes were all friends because that's how good guys should be! ..So reasoned the younger average reader, and so followed the writers.
Before that, heroes were generally pretty asexual, regardless of the existence of girlfriends in their cast. It was easy for anyone to read *what they wanted to* into the character. The same thing that I read as intensely gay, even embarrassingly so, as an adult, as a child I didn't see that way at all. It was just a loving friendship.
Certain writers DID want their stuff to come across as more adult than they could explicitly make them (remembering that they could never actually write Batman gay because GAY was unacceptable--past history as heterosexual is pretty common among gays coming out). Moench has done this with a number of his stories. He is too good a writer to do this sort of thing accidentally.