A couple of girls from my Pony Club parent days grew up to start beginner lesson stables during their 20’s. They used a couple of their own horses, but really depended on the horses of boarders to make things work. Neither was really ready to offer much beyond beginner instruction.
It became harder to find boarders willing to allow their horses to be used for lessons. Both moved on to non-horse employment. My own beginner riding lessons were at a stable where the owner/instructor owned only a single horse. Boarder’s horses were used for back-to-back-to-back beginner lessons, then went back to their stalls waiting on their once every two days one hour turnout time.