Old buildings also go unused because some rich fuck would rather hoard empty buildings when they could be converted into affordable homes for example
And most demolition material ends up in waste and isn't reused, it'd very wasteful to demolish a building to sell the land when some other person is going to build another building out of other materials
Companies claim resources are getting more scarce but they really can't be half-assed to start recycling and finding more sustainable ways to make things
Edit: and companies also do create artificial scarcity of resources they sell to others as a way to Jack up prices as well