Hammerlock hit it right,
any of Diaz recent interviews (several with Ariel Helwani) have eluded to him being all about the money, he wants to get paid. All coaches get paid big time.
The only way Dana got Lesnar to vegas was $$.
As for GSP being the coach last year, he brings big rating because so many people like him. Pair that with a villan (Koscheck or Diaz) and thats TV.
If you look at it from a business standpoint it makes $$ sense.
I would rather see this fight happen in Sept to increase the chance of a superfight in feb, however thats looking unlikely.
If I were to forecast a prediction I would say Bisping vs Sonnen will happen sooner (sept/oct) so that the winner can fight SIlva/Okami dec/jan. If the stars align, I hate to say it but Toronto 2.0 is lining up nicely for next spring.
GSP vs Silva.