Why wouldn't they be allowed to do that?

Ask yourself, if you were offering something for sale or rent, you get to state the terms by which you want to sell or rent it to someone.

And it's up to you whether you want to agree to rent / buy on those terms or not. Reset your expectation about whether to be upset or not.

Unless you're in a rent controlled situation where you're guaranteed a rate/term, you decide to renew the lease each time. Or move.