Ken Wagstaff did it for a summer season at Pontins or Butlins holiday camp, Skegness, just after he hung his boots up, so 1974 ish.
Not saying this is the reason or it's right, but a lot of coaches need to complete hours for their badges etc, especially uefa b level and above.... I know when I was doing mine a fair few people on the course did unpaid hours to get what they needed
A lot of worthy, even essential, enterprises would struggle to function without unpaid volunteers. Always been that way and always will be imo. Right or wrong? Who can say...