The mechanics, plainly.
The most common reverse mortgage is the Home Equity Conversion Mortgage, or HECM, insured by the Federal Housing Administration. It converts part of your available equity into proceeds — as a lump sum, a line of credit, monthly draws, or a combination.
Because you're not making monthly principal and interest payments, the balance grows rather than shrinks. That's the fundamental reversal, and it means available equity generally decreases over time.