To be more exact, individual owners may not be able to sign longer lease terms, especially when starting out. The franchise-based restaurants generally arrange things so that the corporate entity (let's say McDonald's) owns or long-term leases the /land/, and then builds and owns the building, which they then lease-back on shorter terms to the franchisee so they can afford to start/operate the business.

So sure, McDonald's might have a 50-year lease w/ the mall property owner, but the actual franchisee/operator likely has a 1-5 year lease w/ McDonald's for the building + land that's tied to their franchise license.

I allude to this very thing in my prior comment, by pointing out that landlord's incentive to rent-seek in turn incentivizes restaurants to look for longer lease terms.