Welders, especially, are _always_ in short supply.

A few months at the local community college can get you to the point where you can do the most basic welding jobs, but these low skill jobs are the ones that either left the US or got automated, and the few such jobs that remain are mostly done by mediocre welders who should have retired years ago. If you want to do the high skilled welding that pays well, you need to essentially support yourself for years as you develop those skills on your own - and most people who have the means to do so have better opportunities in other fields.

Realistically, employers need to eat the cost of training new people if they want the pipeline to open back up again, but it's more economical to poach a good welder after some other sucker puts their resources into them, so you get a classic tragedy of the commons.

People look at the small difference between pay at the factory or mine (dangerous) and pay at Walmart (not quite as dangerous + employee discounts) and make the rational choice.

During the 2010-2019 US recovery wage stickiness was noticed, even with everyone complaining about not being able to find qualified workers. Companies were very reticent about increasing wages, often preferring to go with signing bonuses.

It is suggested that this reticence/stickiness was because after 2008-2009 GFC many places were stuck with high wages (from the previous boom), and getting people to cut their salaries was almost impossible.

* https://www.investopedia.com/terms/s/sticky-wage-theory.asp

* https://en.wikipedia.org/wiki/Nominal_rigidity

Source: used to weld at the NASSCO shipyard in San Diego.

When welding, you put an incredible amount of heat into the material. This causes it to move in real time. A welder needs to predict how it will move ant actively account for this so that the final piece winds up in the right condition. The tolerances depend on the application - for furniture who cares if it's out a bit, for a coolant line to a reactor you need it to be damn near perfect.

Then there's heat penetration - adding heat to the material changes its material properties. Go too slow and steel becomes excessively weak, go too fast and you don't form a strong bond. Again, big differences between "probably won't break if you sit on it" and "this will kill a dozen people if it fails"

Finally, there's just plain old margin for error. If you're welding together consumer products, it doesn't matter if you scrap one every now and then. However if you're trying to join together two multi-million dollar custom fabrications, you need someone who's going to walk up to this and get it on the first try every time.

I'd compare it less to being a major league baseball player and more to being a professional musician - you can't determine that someone could never do it, but some people are certainly born with a knack for it and you can't simply churn out more on a whim.

In short supply for the wages offered. Bid enough out there, and the positions will fill. Bid consistently such that precarity is avoided and bid even more beyond that, and the bench will deepen. Short supply is entirely addressable by buyers.

There are definitely some industries where the cost to get to the level where you make good money is too high, especially when you aren't sure when you start if you have the required talent to make a great living.

There will always be a shortage of great NBA centres - for reasons outside labour market functioning.

There is only ever a shortage of sufficient compensation to clear the market for a desired level of skills availability.