In reality supply creation is constrained by real world factors such as time and labour supply and "just add more supply" is not so easy. It takes time.
On top of this Airbnb has acted as a sort of friction against supply creation, as when you create a new building, some percentage of the new units were being bought purely to be rented out 100% of the time as a hotel business and were thus never contributing to increasing the vacancy rate. This is why this new policy from the City of Vancouver is explicitly aimed at this sort of Airbnb use. When the City of Vancouver approves a new condo building, which takes years to build, they ideally want 100% of the units in that apartment building available for local renters.