Your Skins Aren't Yours
When you spend money on a skin, you're not actually buying it. In reality you are licensing it from Riot, and they can take it away from you at any time.
You've already agreed to this when you click accept on the terms of service. It's in the fine print the Riot knows nobody reads.
Something to chew on next time you think about spending money on something from Riot. You'll own nothing.