Its not about the Meh pay. It is about the 4 years doing the same work for peanuts without actually learning a whole lot. By probably about the 4th or 5th month of working you will have done 90% of all the different tasks required of you. After the first year, you'll pretty much have the experience that you really need. The rest is just dealing with someone that pulled a number out and said "Hmm, they should work for THIS long".
That might be true in some of the simplest cases - household wiring or household plumbing. But in some of the trades, it really does take several years before they've had sufficient experience in most of the areas that they need to become experts in. I'll used my son as an example. He's been in the International Brotherhood of Electrical Workers for roughly 10 months. Every time he comes home for the weekend, he tells me about all the new stuff he's learned, the classes he's taking, etc. He's never worked in a substation or built a new substation as far as I know; has very limited time working on underground lines. I think that right now, he's doing some sort of transmission line work. That means weeks or even months of replacing 70 foot towers (which apparently sometimes go across swamps.) After a few days of that, he knows all his job duties. And, he'll be practicing those job duties for a long time.
There is, however, the opportunity for shortcuts. Someone can enroll in one of the linesman schools in the country; there are a handful. (I'm not sure what's available for the other trades.) In 4 or 5 months, as you mention, they graduate having learned 90% of the necessary skills. It's not on the job training; nothing productive is being done. Therefore, you pay for that training out of your pocket. (I think it's about $16k)
"Meh" pay?? I believe he started at around $25 an hour and tops out somewhere over $40 within 4 years. So, say he averages $32 an hour for those 4 years... He's already over $250,000 ahead of a college student who has a full scholarship. At the end of those 4 years, he'll be out-earning the majority of new college grads, and that's for full-time work and doesn't include overtime. With overtime, those guys can bring home up to about $9k a week (before taxes.) Of course, it's relatively dangerous work. I'm not sure which is more dangerous - being a police officer, or doing what he does. But, most of the danger is within his own control.