You just don’t get the same exposure at a trade school or through an apprenticeship. Perhaps the real solution is that colleges should offer training in the trades. You’d benefit from classes on how to run a business and do taxes and accounting if you’re in a trade and want to start your own business.
And just because the direct access to the knowledge is not retained, doesn’t mean the residual knowledge is completely lost. If I never learned Calculus I’d have no idea where to start if I wanted or needed to pick it up again, but because I did, I have a much easier time refreshing myself.
As a programmer, I jump from language to language often. When I haven’t used a language in a while I forget a lot of it, but once I start using it again, I recall and pick it up much faster.
So, while those researchers proved that if you don’t use it, you do indeed lose it, they failed to see if a quick refresh of the material proved their skills more than someone that never learned the skill at all. I’d imagine the results would be as I’d expect and those that previously learned it did much better than those that never learned it.
And finally, the author touched on what is more directly the issue. College ciriculiums are simply not well designed. If more majors were designed like engineering as his example, their would be more useful and their for used knowledge acquired during a students years in college and therefore more skills would translate into their field.