Reasons for leaseback requirement on sale?

[Josh Gold]

Single family house for sale, and seller is requiring leaseback at negotiable rate for minimum of 12 months. Seller's agent will not disclose why owner is selling.

At first having a built-in tenant right away sounded great, now I wonder what is going on, and what I am not understanding here. 

What are the most likely possibilities here?  Pitfalls?   Is it common and reasonable to ask seller to put the 12 months rent in escrow at the time of the sale?