A Ph.D. is a union card for doing research. If you want to be a university professor, a principal investigator at a lab, a Chief Scientist or Chief Scientific Officer at a major corporation, then you need that union card.

A Ph.D. program should not be for people who just like learning more stuff. You can take classes, get a masters degree, or just study on your own, if that's what you want. A Ph.D. is supposed to be a certification that you can create an original work of new research, at a quality level that meets the approval of other professional researchers. The research project is typically substantial enough to require years of effort, and the support of others who have already gone through the process.