Why would you assume it's to rent a house? It's a great time to be an apartment renter in big markets like NYC. I just got 2 months free on my lease renewal and I've seen even better deals out there but I didn't want to move.
At least in the part I'm looking at, this was still true at the end of May but is not even close now.
Same here in Somerville outside Boston. There was a giant exodus last year due to COVID and landlords are desperate for any warm body even at a steep discount from the former rent.
Completely the opposite here in Seattle. The rental market is bonkers right now, with very little inventory in places where people want to live. That is very different to how it was just a few months ago.
Isn't that the trick where the price looks good initially and then it goes up wickedly after 12 months because they won't give you free months when you renew?
The price can always be raised at the conclusion of a leasing period so there isn't really any unusual trickery involved. If anything the disclosure that the free months apply only to the first leasing period is less deceptive than raising the rent without any warning upon lease renewal.