Because the man has been working for Mario for several years now. There's info out there about this from people who were talking about BMAC to Georgia before it was public.
Some money better than no money. His relationship with Mario brought him here. His love for Georgia made him leave. That simple (oh, and he knew he'd never be OC here under Mario and Georgia may get him back there faster)
They just lost their WR coach. Come on. They didn't hire BMAC because his time here for a month. He was a known commodity before he came here and worked at UGA