Why is an Oscar winning director willing to entertain Bond in the first place?
I can think of a few reasons.
Every director, and I don't care who he is, has at some point fantasised about making a Bond film. Even someone like Peter Greenaway or Derek Jarman will have at some point or another entertained thoughts of "How would I do Bond?" - this isn't quite the same thing as saying that every director in the world wants to make a Bond film, but I do believe that it's something that's crossed the mind of all - yes, all - filmmakers, even if just as a momentary bit of daydreaming.
Also, the Bond director is a rare breed. There are only eight men walking this earth (nine if you count Irvin Kershner) who can say that they have directed a Bond film. It's a rather exclusive club.
If Mendes - or another Oscar-winning director - were to do Bond, it'd make him look like a more versatile and exciting filmmaker. Unless I'm mistaken, Mendes is currently known mostly as a purveyor of rather ponderous dramas. 007 would be good PR for him - it'd make it look as though he had a bit of spunk and wasn't just an old stick-in-the-mud.
The pay and perks would be - I assume - very good.
Finally, perhaps Mendes has a personal reason for wishing to do BOND 23. Let's say it requires extensive location shooting in China and Mendes has always wanted to spend a few weeks in China. I'm not ascribing such motives to him, but there's a story in William Goldman's Adventures in the Screen Trade about a producer who bought a script set in New Zealand purely because he'd always fancied going there.
Oh, and I'd almost forgotten: Bond is a guaranteed global blockbuster. Mendes will get the largest audiences and grosses of his life. Unless Morgan has indeed come up with a genuinely shocking storyline that's so good that Eon has decided to run with it, it's likely that BOND 23 will be yet another fundamentally conservative piece of good old-fashioned mainstream entertainment, so there'll be limits on what Mendes will be able to "say", but no matter - he'll still be "speaking" to the masses on a scale he's never known, not even with his Best Picture winner AMERICAN BEAUTY. Quite an inducement, as Mr Lazenby said. And Mendes will be able to explore styles and themes that his usual fare doesn't allow for, thus enabling him to stretch himself and hone his craft.