Someone on here hit on the biggest issues with all restaurants, it's the rents. Most of these larger cahins sign 15 to 20yr leases which require them to also pay taxes and insurance. If rent to sales goes about 10% they are in trouble. Most, if not all of these types of leases have 3% to 5% yearly increases, so when a store is in its 12th to 15th year, rent is sky high as are the taxes as they increase with the building's income. Chains will not own the property becuase its an accounting nightmare to take into consideration appreciation, if any. Rent is an income reduction, so its a write off.
Labor is also stupid high. I buy and sell a lot of QSR (quick service resstatuarants) and can tell you that for anyone except the high volume stores, they are paying so much in labor that one particualt chain told me they need to sell a burger at $28 just to break even.
Food costs are out of site, think of what you pay at home today versus a few short years ago. 5lbs of chicken wings for example used to cost about $10 a bag, now they push $20. Ground beef is roughly up $1.50 per lb too. Why? Its our economy in general. Labor, fuel, maintenace, etc.....
Profit margins are around 3% too. It's an extremely stressful and low return business. 10+ years ago when I was working at the (newest at the time) baker's square we needed to make at least $3000 in profit per day just to keep the lights on.