I am willing to bet that most (not all) people that complain that "people today don't know how to fix a faucet" haven't spent hours under a sink, trying to wrestle the stupid plastic (why plastic, since that means it will deform under the least misalignment) nut that's corroded (yeah, neither the plastic nor the brass significantly corroded in the years it's been there, but gunk has migrated into those threads) into place up inside a space you can barely see, using a crappy-ass specialty tool which keeps pinching your fingers better than said corroded slippery worn plastic nut. Have I mentioned the under-sink cabinet space is not nearly big enough to fit your body comfortably into? Have I mentioned that the edge of the cabinet is digging into your kidney or rib the whole time? And did i forget the drip drip of water and sweat and grime making the whole thing even more of a pain in the ass? Oh, and the space you have to work with? Take a look at your kitchen sink. Eyeball the distance between the back of the sink-well and the wall behind it. Notice how deep the sink-well is. Guess what, there is no magic cavern inside - you have to get your hand, tool, light and vision up inside that space to reach the nut. The task itself is simple - "unscrew these two plastic nuts". If it was on my workbench, it would be a 5 second task. Where it is, it's a multiple hour struggle with horribly awkward angles and mystery filth dripping in your eyes.
For those that think I must be incompetent, I'll have you know it took a matter of minutes to put the NEW faucet & nuts in place once I had the old one out and it works like a charm.
It's no wonder people hire someone else. It isn't because we don't know HOW to turn a wrench. It's because getting the job done is a pain in the ass and it is worth the cost to avoid it. If I did the task all the time, I'd work out the little tricks to make it go smoother, and I'd just learn to get used to the filth of it. In the end, I respect the plumbers that do the work, and I say "better them than me".