Why pick out Stirling? OP is a very piecemeal picture.
The biggest towns in Scotland, by population, outside the 4 big cities (5 if you count Inverness), are Paisley, Greenock and East Kilbride. Two of them have poorly supported teams, one has no top flight team.
Meadowbank tried moving to the big new town of Livingston; Clyde to Cumbernauld. Neither attracted any significant new fan base.
Hamilton is an old county town, and one of the top twenty towns in Scotland. Accies have a miserably small support, despite being the only senior club in South Lanarkshire, one of the biggest local authority areas in Scotland.
Club mergers have been attempted. Most have failed. The only successful one, in Inverness, hasn’t led to a well-supported club.
Bottom line is only Rangers and Celtic attract big supports in Scotland. The worst supported, pro rata, are actually Hearts and Hibs, the big capital city teams. In the 1950s, they were bigger than Celtic, regularly winning trophies. But it’s been constant decline since then.