Not many big clubs left outside the top two flights now

[Forest Green Bluebird]

One club that I'm surprised has never been in the the football league is Truro
City in Cornwall massive fan base. Nice city but poor football team.

Large city yes, but it is well out of the way. Difficult to attract anything but local players.

Plymouth, Exeter, Torquay, Yeovil do find it difficult to prosper.

Forest Green is a small 'estate' just outside Nailsworth, but it has grown largely due to the ability to attract playing staff from a much wider and more accessible catchment area.

I cannot think of any successful / big clubs that are a considerable distance away from large populated areas.

Perhaps the likes of Norwich is a counter example.