It makes complete sense to retain him. I may be biased but you can't be looking forward to selling half the side. The club realizes that Rom is leaving, we'll sell Sanchez if any offer comes in, so we can't just sell half our front 6. Add to that, the club isn't sure about Pogba's future and the ruckus he might create. People keep harping about Gomes, but he isn't good enough yet. Chong isn't physically ready to make 30 odd appearances yet for us, atleast based on his limited appearances in senior football. Greenwood is, but they aren't competing for the same position. No one knows how good James will be, and Lingard isn't a mature enough player.
Now, I hope it's not a 3 year deal, but in case it's a 1+1 year contract, it's an understandable action taken by the club