I don’t know if they still do it, but I remember from about 20 years ago that union electricians had one of the most stringent certification/apprenticeship programs in existence. Back then, my late father (who was an IBEW member for about 40 years) was an instructor in their program, and the curriculum was a 4-year apprenticeship before the students could gain journeyman status - and this was not easy stuff either. Significant amounts of theoretical content (think LOTS of math involved) - I would put it almost at the level of an Electrical Engineering degree, just without the calculus that EE required. Honestly, the reason they were paid more is because they flat-out earned the right to it, and personally, any high-level contractor would be insane not to have them on the job.