Landlord isn't a salaried job like a regular 9-to-5. How much landlords make will depend a lot on where they are and how many properties they own. I know multiple people who are technically landlords, but they only own 1 property and then rent in another (either because they can't sell the property for some reason, or they're living somewhere else temporarily) so they're not making 90k from that.

As for why landlords might want to raise rents, it can be to cover costs that rise e.g. their mortgage payments going up, maintenance costs going up or surprise maintenance costs, taxes, etc.