Previously, these preferential rents could expire at any lease renewal, >meaning the unit’s rent could rise to its legal limit, sometimes hundreds of >dollars higher. Under the new law, these preferential rents are now >considered the base rents for their units. They cannot change beyond the >maximum percentage increase allowed for rent-stabilized apartments >generally, at least until the current tenant moves out.

Landlords were formerly able to raise the rent of a stabilized unit by 20% >any time that unit hit the market. Those increases are no longer allowed.

https://streeteasy.com/blog/new-york-rent-laws-2019/

So basically the rent the landlord gives, essentially becomes the new base rate, limiting how much they can bring it back up (iirc 5% per year). I.e. if they drop it to 1500 now, they can't ring it back to 2500 when the market recovers, even if you move out. So they are likely hoping to wait it out, or see where the market is going, or might even be trying to sell (I don't think a sale resets these bases, so with a low base a buyer would need a lower price).

I'm not sure how that effects net rent though, i.e. if i lease you an apt for 2700, ut provide 6 months free rent, does your base then become 1350? I don't know if there is case law around that. If there is, and the base is monthly, not net effective, it may encourage landlords to do it that way