You ask why would anyone do that, yet you have it done to your car? lol I'm a bit confused by that, but I agree with most: It's to give it the retro look.
By the way: The magnetic ones do come rolled up. The one on my car is magnetic, but I had no issues getting it on my car. It was a cheap mod, and looks great. It has a little bit of gloss to it, though; if it was flat black, I'd like it more. If my car ends up in the body shop for any reason, I'm going to get it painted.
However, for $20, you can't beat the magnetic panel! It's easy to install, clean, and cheap to replace. I've bottomed out the speedometer on my car, and it stays on there just fine.