All the bikes in our list have either a 1x or 2x drivetrain. This refers to the number of chainrings on the cranks. 1x drivetrains offer better chain security using a narrow wide chain ring and clutched derraillur to keep the chain on when riding over rough terrain. In order to achieve a wide gear range, 1x drivetrains use large cassettes which means there are bigger gaps between each gear.
Using a 2x drivetrains have smaller jumps between the cassette sprockets giving a faster smoother gear shift. Having the double ring upfront also adds the complications of cross chaining as well.