Madrid has 3.4Mln people and is the second-largest city in the EU. How big do you want it to become?
I disagree on "just build more". There was a time where salaries moved more or less line with cost of living, and especially rents, but with AirBnB and estate funds sucking up any and all places they find, there's an enormous pressure that drives up rents for common people, which already struggle as-is to make ends meet. "Just build more" would simply keep pushing those towards the edges of town over time, while the city becomes a glorified luxury hotel that only rich people can afford. I welcome new regulation to combat this.
I just hope this event shatters any hope for the ultra-right parties that voted against it, and that people remember this. Ultimately, if anyone will build more, it'll still be the large real estate companies and funds that keep increasing rents on their tenants.