Not just Sandy Bell's. The Scotia in Glasgow was a great singing pub, but gradually 'the plague of fiddlers' took over, became incessant, and drove song out! They were so competitive too.
Eventually microphones and formal performance had to be instituted.
Last time I was in Sandy Bell's, I took English friends, and was asked to stop singing after two songs, because a fiddle featuring group were being paid to start. The Royal Oak was more welcoming.