Micky Collins must have impressed people at the club, going from the U21s to the first team and now being given more responsibility as our assistant manager. A guess may be that he was starting to attract interest from elsewhere as well, meaning we had to offer him a more important role to keep him at the club.
I'm sure that the intention is to build a strong staff around Wilder, but IF things don't work out next season, there's an argument that Collins could at the very least offer some continuity by staying on as a staff member, or even take temporary charge. Some great managerial careers can start that way. Alan Knill would probably not offer that, if he'd stayed on in his role.