The skins are created and stored temporarily. Epic would have to make everyone download the skins permanently for anyone to be able to keep them. Otherwise, anyone who hadn't unlocked the skin wouldn't be able to see yours. That also means the download would have to be available permanently for anyone who didn't boot up the game during the event. This feature is not feasible unless Epic makes all of the event skins ahead of time and adds them via TU. However, most of the events are crafted by Pete Nub the week leading up to it. It's a nice thought, but ultimately infeasible.
As for the poll, I like the bonus skins and getting to see them, but I won't ever use them again cuz I always forget to switch back to my normal skins.