Because they found the one person that they wanted to raise kids with and have a house and pay bills and depend that wasn't necessarily their best partner sexually? Have you never dated somebody who was utterly shit in bed but was your perfect match in literally everything else and made you a better person? I mean I personally wouldn't be okay with this and I'd just accept that some things in life are more important than good sex but still... if you can't see why he got married then I dunno fam. You don't get married because you want to fuck that person for the rest of your life. If that's the case I would have been married already... but I'm not because if we had gotten married we'd both be a mess and in shambles. But we'd fuck each other REALLY good.