I think people would see opportunities on the Moon (or Mars) for exploration or claim-staking.
There might be challenges that are hard to resist.
Perhaps they would realize ways to use the resources and experiment with innovations in ways that are not possible on Earth. To make a name for themsleves as an explorer, or gain scientific recognition.
If they hadn't made a fortune yet, and were hoping to do so. Or had made one, and could see a way to make another.
It might just suit a person, in some undefinable way. They might simply enjoy the low gravity, perhaps for health reasons or sport.
There might be things about Earth that deterred them from returning, like war, famine, or epidemic. Or overcrowding, pollution, or debt.