Bristol had a sizeable fanbase, despite having 2 football clubs.
Before "professionalism", players were paid, but they still had jobs. If you were a particular sort of club, you could even arrange for star players to get cushy jobs with local employers to get them to join you! However, since going full-time, the money the club earns hasn't gone up all that much, but the costs have gone up massively. A significant factor in the rise of Union wages in the UK has been the way that the French clubs threw money around. If you wanted to keep your international stars (who make an impact on the gate, and on the compensation from the union) you had to compete with the French clubs and that drove everything up.
The recent changes have brought the salary cap down in England (to £5m), and so there's a strange case that the Welsh regions can pay more for the moment, but that's unsustainable. That's £5m for the salaries for the whole playing squad. You've got to sell a lot of matchday tickets to pay that. Meanwhile football has disappeared over the hills and far away. Some (most?) League 1 clubs will have a larger salary spend than £5m.