To be honest, I think part of the problem is... Both Cass' Batgirl and the Robin series both spun out of two of the greatest Bat family Crossovers, No Man's Land and Knightfall respectfully. Combined with it being the first solo series either identity ever got and this gave them a push that they might have other wise failed to live up to... It's the same with Barman Reborn, there was legitimate interest for the Spin-Offs thanks to the line.