The Bucks reportedly kept Rivers because they thought he could help them keep Giannis.
If Giannis Antetokounmpo departs the Milwaukee Bucks organization anytime soon, it wouldn't be too surprising if Doc Rivers followed. Per insider Marc Stein (subscription required), the move to keep Rivers after last season's exit was because the Bucks felt like it would help convince Giannis to stay. It worked initially, but if the Greek Freak ends up asking out, things could change in a hurry.