There are several reasons why someone might choose to ride a single-speed mountain bike. First, single-speed bikes are very low maintenance. There is no need to worry about shifting gears or maintaining a complex drivetrain. Second, singlespeed bikes are often lighter weight than their multi-geared counterparts. This can be an advantage on long climbs or when riding in areas with lots of mud and sand. Third, some riders simply prefer the simplicity of a singlespeed bike. They find it easier to focus on the trail and their own pedaling cadence without having to think about shifting gears. Lastly, singlespeed mountain biking can be a fun challenge for experienced riders who are looking for something new to try. It can be difficult to keep your pedals turning at the right speed when you only have one gear!