Look, I know a lot of people who are not into that and have super caring relationships and as a result are unhappy. Happiness is such a tricky thing: if you really care about someone and yet a specific part of them displeases you, well, you're unhappy. This doesn't mean you shouldn't care about someone; it does mean that your arguing that caring equals happiness is still gross oversimplification.

But to be perfectly honest, I'm not sure why they bother.

You're just looking at the empty half of the glass. If I were to do the same, I would look at the constant bickering of my neighbors in their 70s and the seeming unhappiness and wonder why anyone ever bothers getting married and remaining married.