In my own experience as an ex ride operator, single riders can be the most un safety conscious of the lot. On rides like Inferno, Colossus and Fury where the Single rider queue was up the exit, they had an almost cavalier attitude to the rides day to day running. I should know, I was one of the Inferno single rider crew and some of the peoples attitudes towards the ride staff was disgusting. Openly rude, telling the staff how to do their jobs and telling off normal members of the public who decided to join the SRQ.
That being said, it shouldn't have been removed from Stealth where it was actually part of the batching design. It all went wrong for rides like Samurai and Vortex where fastrack became more wide spread as I believed it worked well on the flat rides.