I heard whispers that Brian got the job over Emma because he was cheaper.
I suspect this to be a big factor.
The fact that he by winning UBB gives him the honorific title of "ultimate housemate", fondly remembered from BB2 and had a presenting career it seems a good idea but I'd imagine Brian would be cheap and eager to be the decider to have him host the main show,
I mean when was the last time he had a regular TV gig? I think maybe it was his voice on those ads for New magazine were we'd hear him say "read about Kerry Katona's amazing weight loss this week in New" or something like that. Prior to that it was probably that Circus thing on SKY1 that Grace won. He needed the work.