Mountain bike shocks are really the only shocks out there for bikes. You won’t find a road bike with them, because they lower mechanical efficiency, and mechanical efficiency is the entire reason for the existence of road bikes. Mountain bikes concern themselves with other things, such as superior handling in adverse terrain.
The adverse terrain portion of the above sentence is why mountain bike shocks were invented. For a time, a mountain bike was simply a reinforced cruiser bike that ran extra-large tubes on the wheels to attempt to pad the ride on mountain trails. After a while the bikers presumably decided that there was a better way to avoid wrist injuries and loose teeth.
The most difficult thing about the innovation of mountain bike shocks is that they weren’t easily adaptable from an existing product. The closest things to them were motorcycle shocks, and those were still far too massive to be useful in the weight ranges a mountain biker works in. Mountain bikers had to move from modifying existing technology into creating previously unheard of items. This is why the introduction of the front (and later rear) suspension lagged the innovation of the mountain bike itself by a few decades. Today both front and rear shocks are widely available on anything from a good entry level bike up into the top performance models.