I think I mentioned Quizno's. Their decline started around 2006-7. Apparently their business model wasn't franchise fees or a percentage of profits/revenues, but directly selling food and supplies (paper, cups, etc.) to certain franchises. That's not necessarily the business model of other franchise operations, where they buy from approved suppliers. I guess it was all meant to ensure that corporate always got a cut, but it became too expensive for many franchises to operate.
Not sure how accurate it is, but there are some claims that Quinzo's franchises could order from approved suppliers, but that was contingent on meeting certain "quality metrics" via regular inspections. But with some hints that inspectors were encouraged to give lower scores, which would then force a franchise to purchase directly from corporate (which makes corporate more money where they take a cut) as a supposed quality improvement measure. Some claims too that the inspection scores determined the discount that a franchise received on food and supplies.
Most of the articles don't necessarily claim that.
That's when things started to fall apart. The core issue was a simple one: The entire business model of Quiznos was built on a house of cards, and franchisees had been sold a bad bill of goods when buying in. The company made profit largely by selling food and branded products (like wrappers) to their own franchisees; it was how it expanded so rapidly in the first place. But their subsidiary distribution system, under American Food Distributors, sold to franchisees at such high prices that the only way locations would be able to make money was by raking in sales. Since a franchise's average revenue was only around $400,000 per year, that wasn't happening.
In 2006, the dam finally burst when the franchisees started suing them for fraud, treating them as "captive customers" under their distribution system. One even took his own life after the company terminated his franchise agreement for trying to help organize his fellow franchisees for the lawsuit. And that was only the start of the trouble for Quiznos.