Not sure what it is, but I have always had clearly visible, puffy veins. I don't lift weights either, except my own a few years ago (pull-ups, sit-ups and push-ups), before I went to pot and got fat.
I did some lifting (thirty something years ago) when I was in school, but the weights were very light ones, intended more to develop speed while boxing rather than bulk muscle. We also played catch in a circle with bowling balls. That's about as close as I've gotten to weight training. The only "work-out" I do these days is punch and kick the bag when I am either stressed or losing my tactile sense. It helps both of those troubles immensely.
A couple of years ago, my veins were not so visible because I was much fatter, but I could still pop them out. I have lost forty five pounds in the past year and a half.
YaY!