I have a lawn tractor with hydrostatic drive, if that counts
The number one reason that comes to mind is efficiency. Somehow, you have to spin a hydraulic pump, and the hydraulic fluid, in turn, spins turbines resulting in mechanical energy that can go to a gearbox of directly to the wheels. That is, in effect, a multi-stage system. Every time you convert energy from one form to another, you are losing some of it to friction, inefficiencies of the process, etc. No machine is 100% efficient. Even a 90% efficient electric motor, for example, spinning a hydraulic pump that is only 90% efficient, that is pushing it's energy to a 90% efficient turbine/hydraulic powered gearbox...90% of 90% of 90% is about 73% or so...each step in the energy chain lessens what you can get out of a system.
As far as dynamic range goes, there are a few problems, the viscosity of hydraulic fluid being a big one. Offhand, I seem to recall that very thick fluids aren't well suited to high pressure situations, and there are issues (lubrication?) with thin fluids, as well. Dynamic range implies the pressure being variable from relatively low to relatively high. However it's achieved, it will create a lot of heat in the fluid, inevitably, and whatever is creating that pressure won't exactly be sittin' cool, either. That heat is lost energy.
The advantage of hydraulics is you can use a relatively small, underpowered engine, and by mating it to the right pump, line size, and rams (or turbine and gerabox), you can push a major sized hydraulic ram, or produce a ton of torque...with nil horsepower and/or dynamic range.
Engineering types, please feel free to correct me as needed.
