There are a large number of policies, including the one being discussed in this thread, that individually don’t move the needle much, but when combined will move the needle in the right direction. However, every single time one of these policies come up, the above argument is used to oppose such policies. “This won’t move the needle on housing, and it will inconvenience me, so I oppose it!” So the policies don’t get enacted, or get neutered, and then the needle never moves because nothing ever gets done.

There are millions of people and hundreds of thousands of homes in the greater boston metro area. Any developer trying to fix prices is just going to be undercut by another developer to make money. The market is too big for the type of collusion (at the scale of the whole region) you are describing.