Shorter, cheaper to maintain - had good commuter potential being an almost straight line route unlike the snaking Port Erin line.
It was closed in the 60s because it didn't have the same traffic as the south line to Port Erin. Once it was closed and the line was lifted that was that. If it had limped on another five years we'd probably still have the Peel line though.
The south line only survived by the skin of its teeth, it was cut to the section south of Castletown for a brief period. I always get the impression what really saved it was the rise of Manx national pride in the run up to the 1000th anniversary of Tynwald celebrations in 1979.
The line north of St Johns to Ramsey via Kirk Michael was always a basket case.
As for reinstatement, the trackbed is intact from Quarterbridge to Peel. But I'd vote against any MHK who seriously suggests it in their manifesto. It has more value as the footpath/cycle path than it ever did as a railway line.
The railways now are tourist attractions, they serve no purpose for commuting. But it's worth noting the buses to give you an idea of the market: it's 3bph from Douglas to Port Erin, 2bph from Douglas to Peel and Douglas to Ramsey via Laxey, but only 1bph from Peel to Ramsey via Kirk Michael.