Well you could ask why didn't he join West Brom then if he wanted a real challenge.
And people can't criticise him for choosing the "easy" option and be in the team every week at Chelsea when they criticised Nasri for going to City to be a bench warmer.
And the fact he's been trying to engineer a bidding war to increase the wage offer is simply rational behaviour. It doesn't mean he lacks ambition. He's joining the Champions League winners afterall.