I agree that salary and the Paris lifestyle are factors. I'm sure both of us - and objectively, most people - would prefer to live in Paris than Manchester.
Of course, United is still paying Pogba a very healthy salary, which will eventually increase, and I think the sponsorship opportunities playing for a team like ManU are likely greater than they would be at PSG. Either way, the guy still has way more money than he can reasonably spend.
I despise United, but I don't think they're a crappy club atm. They've been in transition since Fergie left, but they picked up more silverware last year than PSG (kinda validates Pogba's decision to this point), they're 2nd in the league right now, and they have as much exposure as any club in the world, really. Despite Jose constantly moaning, they still have serious buying power, basically right behind PSG and City. Anyway, Pogba saw an opportunity to finish what he started there, and I get the rationale behind that decision (although I really don't like how he handled that process).
I actually think Juventus would have really had to push him to select his 3rd most favourable offer. At that point, it would have had to be mostly about cash.
PSG haven't won anything but domestic titles in recent years, and most people still tend to rank the French league as 4th best. I think for the vast majority of players given the options of United, Madrid, or PSG, England or Spain take the cake.
CL is such a crapshoot, anyway, it's impossible to bank on that. It takes a great deal of luck, and team cohesion to pull that one off.