It’s because every dollar you pay off your mortgage is a dollar you get back when you sell the house. All of that 3K you paid renting is lost every month, but a sizeable chunk of the 5K you’re paying is effectively going into a high-yield investment account which you will “withdraw” by liquidating the asset (ideally). Even if the home value doesn’t grow incredibly, so long as it doesn’t lose value you’re still saving a ton of money over a long-term horizon.