At one time Snowmobiles only used mechanical reverse like ATVs until Ski-doo/Rotax came out with "Rotax Electronic Reverse" (R.E.R) in the late 90s now everyone has copied and uses it.

The electric reverse has no down side ,because its just a push button that retards the ignition and runs the motor back wards.
You get a lighter smaller tranny without the reverse gears,no wear and tear with mechanical parts engaging each other(Grinding) or linkage rods or shifter positioning for reverse,just push a button.
RER has proven to be super reliable,but even if it goes its just a $400 for a new RER ignition kit and it can be added to older snowmobiles that never came with reverse in the first place.

Here is a Polaris reverse kit but you can disallow the scondary clutch and ram its a buy once item and a Tac is opional because RER only engages at idle,I have seen sleds with RER that have no tac. That leaves the rest which would be lucky to weigh up to a 1/2 pound.

Just can,t see why the ATV world does not use it.