The most important causes is the massive increase in travel/tourism (airbnb is often pointed, but regular hotels are where it started) then come the increasing cost of labor (Baumol's costs disease) + higher safety standards for both the inhabitants and the workers (this includes DDT but not only) + higher living standards (people have bigger apartments with more stuff in it), which makes house decontamination much more expensive that it used to be.
Decades later with no comparable eradication strategy, and once world travel increased exponentially, they have been reintroduced from parts of the world where they have always thrived.
I seriously doubt this is the case in Paris
You can find quite a lot apartments that used to be two smaller ones that have been merged together, especially in the upper floors.
