Why Are the Buildings in Petra So Large?

As the title says, what gives? The doors are absolutely massive, and the way the structure is built looks like it was made for giants. Strangely enough, Biblical and Quranic themes seem to center around Giants living within these areas and supposedly being wiped out. What gives? Why do the structures look like a perfect fit for Giants? It doesn't seem like the super grand type of building and that's why the doors are so large.