You spend time and effort when you are younger (eg 15) to develop skills that allow you to be productive and valuable.
Learning entirely orthogonal skills when you’re older no longer pays off after a certain point because the opportunity cost of not using your existing skills to produce becomes too large.
To make an extreme analogy, there is no point in Warren Buffet to learn to program at his stage of his career (or even 30 years ago). Any time spent not reading financial reports is such a huge opportunity cost that he really has no reason to learn any other skill.
Another extreme example is Lang Lang the pianist has no reason to pick up the violin. He has absolutely nothing to gain by learning new musical instruments.
Science is a special career where learning new things is important for longevity. A productive science career involves breaking new ground, picking up the low hanging fruit before your competitors do, then move on to break new ground once your old field becomes saturated. Learning new things is strategic, where you try to leverage existing expertise to break ground in new fields.