You're incorrect. If interest rates drop, then the value of the mortgage increases. But without that, you're getting a return from the interest of the mortgag

You're incorrect. If interest rates drop, then the value of the mortgage increases. But without that, you're getting a return from the interest of the mortgage. If you have a strip bond, where you pay a deep discount to the value of the bond, with no interest payments, then your bond does indeed gain value over time.