I don't know how many studies have been done on this, but I have a conspiracy theory that it's a tradeoff for becoming more analytical and STEM minded basically. The number of STEM jobs have exploded in the millennial and gen-z generations, especially in the West where most of this stereotype seems to be concentrated in, which deal more with abstract thinking and memorisation as opposed to working with your hands and very high motor coordination, as is required in things like manufacturing or agriculture. We just don't train our muscle memory as much anymore due to a higher likelihood of not really having to anymore. (Which I guess also implies the inverse of the stereotype of boomers "being stupid" and prone to not thinking of the long term consequences of things being due to a much higher proportion of them working more labour focused jobs where analytical thinking is less important so they could just forget all the things they learned in school. I mean it's surprisingly common too see boomers thinking stuff like "windmills cause cancer" or "vaccines cause autism.")
I also firmly believe that you can get better at both analytical thinking and working with your hands if you make an effort to practice (don't practice by driving distracted though). The brain is highly adaptable regardless of your age or upbringing.