That's it. That is way cooler for a French to go in London than Paris. Especially, if it does not work out for him he will just come back with a solid resume that will get him a comfortable position easily.
Like he decided to live in Kengsinton. Sure he share, like most singles in London, but he tries to live the life and was not too successful (yet, hopefully for him).
Concerning expatriation, I think many people want to live abroad just to experience a different lifestyle. It's not always about taxes.