There are plenty of people that want to be electricians - the schools only accept so many applicants. It's the same issue with the artificial doctor shortage - artificially limited supply to keep wages high.
But are the schools artificially limiting their intake, or have their own resource shortages? If the former, what do they gain from doing so such that any individual school can't decide to it's better off accepting as many students as it can?
In the case of medical schools, it is controlled by the AMA. For electrician schools, it is the unions. Both seek to keep wages high and the only way to do that is to gatekeep the credential process. Remember those that teach at these schools are doctors and electricians that benefited from the controlled system. It is the reason programmers will never have a union and accrediting agency because corporations want wages to decline, not increase.
For electrician schools, it's funding and personnel (read: funding).
An electrician is doing hands on stuff in a lot of labs. That limits the student to teacher ratio that can be sustained. So, you'd need a lot more teachers who are already certified as electricians to come teach. Are you paying them enough to get them to come teach as opposed to work or manage? (LOL--teachers always get paid absolute dogshit).
After your first year of training, the expectation is that the apprentice is getting paid. So, you need to have some companies willing to cough up to pay more for the increased number of apprentices. Who is incentivized to do that?
Want more electricians? Bump the pay to $100K/year for a journeyman. You'll have lots of people wanting to be electricians.
That actually is about the average salary for electricians in Australia (though I would imagine not for those just starting out). And we still have a shortage, reportedly due to not enough students enrolling into apprenticeships.