If someone asks me why do a PhD, I think I know exactly what to tell them -- to become the horse breeder.
A solid amount of my time as a PhD student is spent thinking about thinking. In the horse breeding metaphor, which Sabine Hossenfelder attributes to Steven Weinberg in her book,
The horse breeder has seen a lot of horses, and now he looks at a horse, and says 'That's a beautiful horse' when from experience, he knows that's the kind of horse that wins races.
A researcher's life is no different. Among various competing theories, one must pick the one that may explain the data, and perhaps the reality. But choosing to pursue a theory comes at great cost in terms of the mindshare of the community. The hallmark of a seasoned researcher is to pursue theories that, more often than not, lead to significant progress -- their beautiful horse.
Of course, I don't think one needs a PhD to become the horse breeder. This principle may be better advertised for life in general.