I wouldn't say that the demand for short-term rentals is so much higher than that for long-term ones. I'd say that landlords know they can make a lot more money with short-term rentals, and that's why they do it. The rentals don't even go to the long-term market.
I know that's partially the case in Ireland of why it's so hard to get housing. Landlords can make a full year's rental salary over the summer with AirBnB...Why rent long-term when you can do that?