Meaning - keeping Stewart means a scholarship for 1 year.
Bringing in Davis means a scholarship for potentially the next 4 years - and maybe longer if there's an RS or injury.
I'm not saying that was the deciding factor, but I could see an incoming coach thinking he wasn't going to be able to turn the entire roster over in a year, so keeping seniors who will only stay for one year is an easy thing to do. If you've got a certain type of player in mind for your system, bringing in a player for 4-5 years who you don't think is the best fit is a different consideration.
That's without making any judgement as to the type of player Davis is - I'm just saying there could be an explanation that makes sense depending on how Young sees Davis fitting in.