Because long-tube's won't pass emissions when required. They are designed to eliminate catalytic convertors which is also illegal in a few states, not sure about the age of you vehicle and if it is "required" to have a cat.
Painting them is super simple. Put some tape over the entire flange so you have a clean mating surface and so no paint get's down into the primaries, then go get some VHT paint in your choice of color that is rated for exhaust temps at AutoZone, Advance, NAPA, etc. and start throwing on a few coats. It's easy to do in your garage. Just grab a metal coat hangar, bend it to your liking so you can put it through a bolt hole, and hang it from the garage door rail. It will not only make them look better, but it will help in keeping them rust-free for years to come :thumbup:
Just my $.02.