[Nickj]

Like the hydraulic brakes introduction the hydraulic clutch took off and one of the given reason was easier pull than cable-actuated clutches. It was also a new and exciting selling point. As Mr Gaza says the cable is the weal part of the system and the liners no matter what they are wear and get glitchy.
A side effect of the easier pull allowed the use stiffer clutch springs, making the clutch stronger and handling more torque. Given the power outputs of modern engines you'd need a more complex arrangement that a long lever at one end or the other to give you a good chance of pulling the bar lever in.
They are also able to provide a more consistent feel than cable-actuated clutches and they do simplify the manufacturing process though I'm not sure how but KTM for one says that they do. Instead of a cable pulling on an arm to actuate the clutch, the hydraulic system obviously uses a clutch slave cylinder and a push rod, and they can be tucked inside the motor casings.
The hydraulics do need bleeding but once set it stays pretty much the same and doesn't need to be tweaked as the clutch wears or the cable stretches.
And you can change the slave or master to tweak the hydraulics feel and pull weight.

Also as Mr Gaza noted you won't get your nipples pulled off, possibly the best advantage as it's potentially painful ..