We are building, but building takes time, and all the houses and apartments are bought by 'investors' that then use them for airbnb... This is even more true in places like portugal (and many others), where realestate prices are so high compared to normal peoples income (due to speculative and airbnb investments), that normal people cannot afford them anymore, and only people with a lot of money or other realestate (for mortgages) can buy them, and the best way to earn back investments is again, airbnb.
So, you need to both build new stuff and ban airbnb for any chance that normal people with normal incomes will ever be able to afford to buy anything decent to live in. Also somehow stop buying realestate for investments. Also fix zoning laws in many places. Also...
Building more housing just to satisfy speculative demand never ends well. You get ghost cities/districts and lots of pink elephants; and when the bust comes, its a huge mess to clean up, and a lot of those units will never be used before being torn down.
So, you need to both build new stuff and ban airbnb for any chance that normal people with normal incomes will ever be able to afford to buy anything decent to live in. Also somehow stop buying realestate for investments. Also fix zoning laws in many places. Also...