These bistros (as culture) are like newspapers and media in general, where a high quality middle ground is no longer viable, so only the very cheap, and the very expensive survive, and the middle is hollowed out.
Arguably, a quality middle is the effect of a temporary distortion or disequllibrium, where for whatever reason, quality has not been optimized out of an attractive price point. A good middle quality bistro doesn't compete on marginal price, it seeks to differentiate itself on features.
Customers become indifferent to the feature quality, select for price, and good places fail. When you add tourism, you add feature-indifferent customers who select on price - which is why locals hate them, as this indifference upsets the local equilibrium that made a good middle possible, and that hollows out their quality of life.
The same quality is available, but it costs more to sustain because it has lost the price selecting customers, and must survive on a smaller population who values them.
This was the big "race to the bottom" criticism of globalization in the 90s, where global competition ostensibly ended local ways of life by flooding markets with indifferent consumers of goods optimized for generic global markets.
Polarization happens, and it's usually costly regulation that staves it off. France led the way with designation of origin (controlee?) trade rules, and banning the McDonald-ification of their cafes probably has precedent.
Rents and real estate prices are the other key factor, where the risk/reward for anything but a proven franchise model is not a viable investment. San Francisco is a great example of that. It's not gentrified, it's globalized.