INMO................
They may have turned into "bad mechanics" due to poor supervision during thier later years as an apprentice,they lose thier passion/enthusiasm for cars,
rush up - f@%k up attitude of the work place management or they get lazy and just dont care after a while and are not willing to change.
I've seen many great mechanics get screwed over quite badly by management that their quality and or quantity go right out the window and slowly start to screw the business of which they eventually leave to go somewhere else, or they leave the trade altogether.
For example; I know a bloke who has been in the trade for 35 years, had up until a few years ago ever been employed with this one particular brand, worked with many rally teams around the world including the world rally team of this brand, could rebuild a gearbox, including in and out of the car in 2 hours and an engine in 4 hours. He wasnt on much more $$$$ than myself, so rightly so he asked for a pay rise, was told they would review his work times etc, etc .....then got told no, so from then on he did all the work to the time allowed be it warranty or retail, then got grilled about why he wasnt putting the same effort into his work, his reply was .........................
"Do you really need to ask me this question?
im doing it to the time allowed/given, no more and no less.
Has thier been any come backs due to my workmanship?"
management answer "No".
Anyways he left about 6 months later once he had set up his own workshop and many of the customers from that "workshop" now go to him.
Oh his quality and quantity came back once he left......funny about that
Well I guess that is safer than not wearing one at all.... 
Some of us are also obsessed 
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