In the past 7-Eleven was unique in the franchise world where you could make a comfortable living owning a single store and that was the major ownership model. McDonalds and other options at the time really depended on a multi-store ownership model. Corporate 7-Eleven (Southland Corp technically) moved away from this single store model in the mid to late 90's, instead preferring single, larger corporations in a region, owning 10+ stores over a single store owner. They made this happen over a 20 year span by changing the contracts franchisees sign and must to re-sign every x years. Every contract renewal drastically reduced the single store income and made it much harder for single store owners to make a living. Corporate also started preferring to give new stores to existing, large scale franchises over new store owners which changes the initial capital needed for a store by over 10x as with an existing store you will have to pay the rights from the previous franchisee instead of just the corporate.

My parents, grandparents, aunts and uncles all own or have owned 7-Eleven stores and have since the 80's. I've worked there, been to their conferences, and still get to hear about them at all family gatherings :)