This article suggests that due to climate change more people are trending toward off-season travel.
https://www.cbc.ca/news/world/europe-mediterranean-travel-future-climate-change-1.6912589
Selfishly, I'm hoping it's only a blip in traditional habits. I enjoy my April/May and September/October trips and don't want to share it with others. How early or late in the season are you willing to travel and put up with poorer weather?