I want to be a second landlord, but many landlords are unwilling to rent their own houses. How can I convince him?

You have been passive! Your statement was wrong from the beginning. You shouldn't just tell the landlord what you want. Obviously, you can't talk. Discuss with him in another way, for example, I rented this house, but I have a cousin coming to live for a while, and so on. You don't want to think about it either. You made it clear that any sick boss would agree.