We don’t really know why they are coming back. But the fact that they used to be everywhere less than a century ago should make everyone think about protective strategies, instead of thinking that they are someone else’s problem. This is not “lol Paris” (or “lol AirBnB” like some say in other posts), this is a Europe-wide public health problem in the making.
AFAICT the number of infestations grew 65% in a year in the UK. A couple of years at that rate and even if you’ve never seen any yet, you are likely to know them intimately.