Can a skin be the main reason why someone plays certain champion?
I will give an example:
The main reason why I started to play Fizz was because of his Void skin. I love the Void and and even though I purchased and started to play Fizz before this skin was even released, this skin was the main reason why I played Fizz much more than before and I had the desire to master him. The result is that Fizz is nowadays the champion I use the most on ranked games, and according to some sites, Fizz is the champion that I have the best overall statistics. I don't consider myself to be a main Fizz, though, but I love playing him.
I also purchased and managed to learn to play Gragas just because of his Santa skin. Although I don't play Gragas nearly as much as Fizz.