Because I don't have to carry the sunglasses with me all the time?

98% of my time I'm not in a car, and my not mediocre sunglasses work better than the clipons, since I prefer the color, they already block UV and aren't too dark.

Why should I carry something else?

As it is, I put my glasses on when I wake up, and most days only take them off to clean them or go to bed. They're almost hassle free, unlike carrying around sunglasses, putting them on, taking them off, yada yada , like I did for 10 years before I got transitions.

Why do you carry a smartphone, instead of a laptop, tablet, feature phone, GPS, mobile access point, multiple credit cards, rolodex, checkbook, etc?

It's funny you trying to tell me that I'm wrong to choose what works for me.