This tendency started long before airbnb and foreigners started buying a "big majority of properties".

People have been moving to cities for decades now. Many of humanities recent developments make much more sense at scale so people are going to places with that scale. Some prefer a quieter environment and don't move but most people rather have opportunities, jobs, services, etc and all that is made much easier when lots of people are concentrated in a smaller area.

That's true, but at least all these places were kept unharmed and less touristic before airbnb. Each island's tourism was almost limited around hotels and established rental houses before. Airbnb opened up the gates for that extra income for anyone having more than 1 property, these side businesses, building, renovating, managing, cleaning, selling around airbnb. And if you are a rich foreigner, you can buy properties everywhere in the world and keep making money from that local tourism.