"Why would we want to start run company anywhere else?"

Rent? And living expenses in general. It's going to be you largest expense bootstrapping, especially since it's post tax. It also gets harder to invite people you know to come work with you and getting a larger/better suited apartment in general (location, contract terns, layout, furnished etc).

Not that this is that different from other big cities and I personally think Paris is one of the few that lives up to the hype. Still not preferred for early startups.