This is my first post, but thought I would chime in as this is a very interesting topic to me.
The repair industry is in the same boat as other industries like manufacturing and farming. We can simply get more done with far fewer people. 30 years ago, every town bigger than 2500 people had a transmission shop, usually more than one. Rebuilding your cars automatic transmission was something you could count on doing multiple times in the life of the average car. Same thing with engines. If you put 100,000 miles on an engine, it needed to be rebuilt.
Today, things are much different. Cars routinely go 200,000 miles without even changing the spark plugs. The odd transmission or motor that does fail will just be swapped for a remanufactured unit that was rebuilt in a large factory in an assembly line style. I would be amazed if the average auto dealer mechanic ever does any kind of engine work more complicated than changing a head gasket, and there is likely only one or two guys in the shop who can handle that task.
It's essentially the same thing in the world of heavy equipment. 30 years ago, if you got 10,000 hours out of a diesel engine you considered yourself pretty lucky. You would take it down to the local dealer or machine shop and have it rebuilt. Today, we can get 25,000 hours with a few valve adjustments and maybe and injector or two. When the motor does fail, everyone today is in such a hurry that they can't wait 2 weeks for their motor to be rebuilt. They will swap in a reman unit for roughly the same price and be up and running a little sooner.
I know the local Bobcat dealer and the local Kubota dealer don't have anyone on staff who can do internal work on an engine. They all just swap them. In this way, being a mechanic has gone from diagnosing, disassembling, ordering parts, and rebuilding to just changing out components. IMO, it's a real dumbing down of the trade.
10 years ago I worked in a truck repair shop. We did in-frame engine rebuilds and transmission and power divider rebuilds in house. But, we never worked on heads, we just bought reman heads for every engine we rebuilt. There was not a single guy in the shop who knew how to install a valve seat or run a valve grinder. Once in a while we would replace cam bearings. If an engine spun a main bearing, we just swapped it with a reman. In that 6 man shop, there were only 2 guys who ever did any engine work.
So, manufacturers have made great strides in reliability meaning we need less mechanics. The move is toward swapping components for reman units meaning the mechanics we have need less skills. The result is that mechanics are feeling their wages being squeezed. The old guys who can do component level repairs are left working on older equipment that is not supported by the reman industry. The problem there is that folks aren't willing to spend as much money on that old equipment.
That leaves mechanics in a tough spot. It's hard to negotiate higher wages when the industry is making it possible for lower skilled guys to get the job done. There will always be a place for the highly skilled (and highly paid) guys, but we will need fewer and fewer of them to keep the wheels turning.