I think it's all tied up to a long running saga about a new 'Stadium for Cornwall' to be built in Truro as the club there was making a go of rising up the leagues and had some success with that.

The more controversial element is that Cornish Pirates, who are pretty successful, plan to move from Penzance to Truro to share the ground. Amidst all the drama I guess Truro City fell into difficulty and got bought out by the rugby club and temporarily moved to Plymouth. Not sure why they themselves didn't temporarily relocate to Penzance where the rugby club currently play.

Either way, I don't think people in Cornwall have much of an issue supporting Plymouth Argyle which is on the Cornish border anyway. Rugby is also pretty big there.