Well ... It takes four years of education before becoming a taxi driver in London: https://thetaxi.academy/
It takes also many years of study before they will let you touch any living person with your scalpel, and then many years of apprenticeship with actual surgeons when you do touch people with your tools.
I can imagine maintaining a big jumbo jet also requires some specialized practical knowledge you cannot acquire just by reading books and looking at nice little videos.
The problem is not to explain things when everything works perfectly. The problem is getting the ability to diagnose the root causes of defects using all your senses and your intuition. That is not taught in books.
There are detailed step-by-step instruction cards (task cards) for every single maintenance operation on an airplane. Nobody is reinventing the wheel, they’re carefully following predetermined procedures. Someone has to figure out which maintenance procedures need to happen, but the work itself is laid out for you step by step.
> It takes four years of education before becoming a taxi driver in London
That doesn't apply to private hire vehicle drivers afaik.