I dont think mattress stores are typically getting long term (20 years) leases. Usually those long term leases are for anchor/grocery stores with credit. Now maybe 5-10 year leases with renewal options but typically renewal options are at fair market value so rates reset based on market at each option. Second, leases typically have escalation clauses where rent steps up over time. Of course market rents could outpace the stated escalation. Last, sublease rights usually need landlord approval and any increased rents from subtenant are shared with the landlord. Sophisticated leases will also have landlord recapture rights if tenant wants to sublease. Are there situations as in your example, sure but sounds like mom/pop unsophisticated owner.