I'd imagine it's mostly a question of having the freedom to be able to work upon subjects which very much interest you, independently and on your own schedule, without much outside pressure or coercion to produce tangible results that are useful to anyone but yourself.

There may be something to that, at least according to one study. Specifically, this article [1] indicates "embracing new mental challenges may be the key to preserving both brain tissue and brain function."

[1] https://www.health.harvard.edu/healthy-aging/what-does-it-ta...