Because its a bloody good laugh. It also changes how you ride, you adopt the 'just get on with it' style.
Recently converted an old carrera fury as gears knackered just for fun. Its quite satisfying removing everything but the brake levers off the bike. Fitted 36/18 as it seems a ratio of 2 to 1 is advised as a good starting point. But if you look at the american forums on the subject, most of them seem to go lower for the hills and technical bits. It seems to be a big scene over there with some lovelly looking bikes in the galleries.
First thing that struck me was the directness of the drive, you could feel the crank doing some work. Also the quiet on even rough tracks was great. Took it with me on vacation last year for a bit of fun and was surprised what could be done off road. Dropped the back wheel into a couple of gullies that would have definitely ripped off the rear mech, so that was quite a good feeling.
The only big draw back is actually level ground, spinning like hell doing about 13mph. But just need to accept it and enjoy the ride. Also i guess it won't be ideal on steep/narrow technical bits as you can get bogged down. But i am someone who doesn't mind throwing bike over my shoulder and walking it, as i only do it for occasional fun and i do enjoy hiking anyway.
Overall, we shouldn't get too hung up what is best ( 27 or one speed). I think a ss mtb should be a bit of fun and a great way of breathing life into an old bike.
