Source: I spent 7 years of my life getting a Ph.D. in physics. By the time I got the Ph.D., the only reason left I had for finishing was because I'd started.
A Ph.D. in almost any technical subject (including, but perhaps particularly Physics) is a credential that shows you can dive deeply into a complex problem, demonstrate inventiveness and independence, not give up, and come up with a comprehensive report (dissertation) that describes what you accomplished.
It can be hard to finish a Ph.D. on a project you have spent years on, and may have lost interest in. I'm not surprised you finished your Ph.D. in the end just because you started it. Many people finish just for that reason, if they manage to finish at all. But be proud that you are among those who did.
[Disclosure: yes, I have a Ph.D. in Physics too, so perhaps my bias shows.]