Trading in a lease?

I have a leased Kia that ends in 6 months. I found an almost identical car for sale with a price MUCH lower than my residual/buyout.

The dealer is willing to assume my payments and sell me the new car. Sounds great for me.

My question…

Why is a dealer willing to do this?

Is it all just a game in the residual/financing? Is used market hot enough that they know they come out ahead?

I just want to understand before I sign on the line.

TIA