maintenance on older stuff is mostly simple
try any of the common rail engines. U can't even SEE the engine, all you see it junk piled around it
doing a valve adjustment on a 4701 for instance? Remove: DPF assembly normally, fuel tank, some of the wiring harnesses, i can't remember but I think injector lines, brackets, hoses, hood, loader, THEN you can "see" the valve cover....takes roughly 5-5.5 hours for me to do it, I don't work all that fast on bigger jobs. Then there's fluids and gaskets that might be needed.
....and those are pretty easy in comparison. L3301/3901 are similar, just start taking stuff off until you can find the valve cover. Then take a break, stand there and look at the pile of parts you just took off, and wonder how on earth you think you're gonna get them back on and not end up with spare parts. Some of the bigger ones have 4 valves per cylinder, not that they're any harder, just more stuff to deal with...like injector lines going through the valve cover, etc.
THAT is one or two reasons why owners pay the dealer. Sometimes it's because they trust the factory-trained techs. Sometimes it's because they don't have the spare time to set aside a full day for servicing. Sometimes it's because they dont' want to have to deal with the hassle, like having to figure out how to dispose of 5-20 gallons of fluids, several filters, etc. Other times, it's because they don't have the tools or know-how. And oftentimes, people paid me/us to do their servicing because they could write it off on farm or business taxes.
place i worked for also had powersports stuff. You haven't lived until you have to do a valve adjustment on a crotch rocket. 20 valves packed into a cylinder head that is maybe 10" in length, 5" wide, and all 20 of them buried down in the head so far that you have to creatively make tools to reach in there to measure the clearance....and if you have to adjust? Remove camshafts (tensioner, chain, etc), change the shims, then try again. If you don't get it right, remove camshafts again and repeat until you get 'em where you want them. Of course that's AFTER you disassemble half of the bike to even access them....only job harder that I ever did was basically any engine repair on an SVL or SSV.
They aren't making them any easier to work on, which is one of many reasons I still say that a gasoline engine would be a better option for a lot of folks. Not all, but many.