What’s wrong with getting married for money? As long as your upfront about it and the other person is ok with it then what’s the problem?
If both people are onboard, its okay I guess. However, I imagine someone that is rich and okay taking on a partner with no love in relationship is going to have a lot of choices of people to pick from for the position of "stay at home partner". I'm guessing that you'd have to bring a lot to the table to win out over your competition. If I were not the rich one, I'd also be worried about the end-game. A soon as whatever got me the rich partner fades, what would prevent my rich partner from dumping me and trading up to someone that has what I had years prior? You can bet anyone rich will make you sign a prenup, so you won't be walking away with very much when it ends.
The deep loving relationship is what keeps partners together long after looks, charisma, and cognition fade with the passing years and advanced aging. Getting old sucks for everyone and there's nothing we can do to escape it. Getting old alone without my loving partner sounds like hell.