It's kind of ironic. Trades and the like have constantly needed more people, so the equipment manufacturers have made improvements on the equipment and materials to make them easier to put in, and trades people have adopted those improvements to save on labor. The flip side is it has become fairly easy for people to do the work themselves or for a less specialized handyman to do it. Mini splits are fairly simple to put in. Basic plumbing has gotten stupid simple with PEX and push fittings to transition from copper to PEX. Hell, they make all in one tankless boilers now. As long as you aren't an idiot and can vent it properly and double check your gas fittings for leaks, those are fairly trivial to put in. A lot of this stuff used to cost a dozen or so many hours, usually hundreds or thousands in labor, and now they can be knocked out in an afternoon by an accountant or IT guy with a $200 set of 5 power tools from Home Depot.