Earlier quoted context omitted.
Hard to say. It could be a million things. Some people are just hard to get along with. Some people are great fun for 1 hour a day, but miserable if you're around them all day. If you've devoted your life to your career, it's no surprise that you won't have anything in common with your wife & children, which makes things harder. They may love & respect each other, but not find each other's company enjoyable.
I've known and talked with enough people to know that you are very likely right -- that still doesn't stop me from thinking "how the hell can love and respect exist in such conditions?" People are extremely diverse indeed. I've known such couples and couldn't for the life of me ever imagine me being in such a relationship. But they are out there.
Not all conflict is borne out of character flaws. Put me in the same room as an extrovert - be it in a workplace, boardgames night, or whatever - and I'll appreciate and respect their ability to keep the conversation flowing naturally. Put me in the same home as an extrovert, and that same habit will drive me mad. I need my occasional peace and quiet to recharge and focus! And perhaps just as much, they'll need someone to keep talking!