>Why isn’t a year upfront incentive though?

For one thing its actually illegal

Landlord tenant law is chock full of things that the parties are prohibited from agreeing to do.

Sure, you think you are "volunteering" to pre-pay (so it's not the landlord "requiring") but if you can volunteer, why wouldn't a landlord refuse anyone who did not also volunteer that?

The law strictly limits what a landlord can accept in advance, because what they can accept is in practice what they can require.