I can tell you exactly why, in exactly three characters: F, 2 and P.
When you have an F2P game, your income comes from nickel and diming people into infinity. You don't get money from people playing and enjoying your game, and you don't really care how long they play so long as they throw money at you. League is an F2P game, and as such, they don't make money anywhere but from the cash shop. Whenever something pretty comes out, they'll make you pay through the nose for it (you can grind for champs, but if they didn't let you do that, the game would be P2W), or make it so unbearable to grind for that you'll just HAVE to spend money to get it.
There's a reason I typically avoid F2P games like the plague. >.> It's a horrible business practice, and it's all a great big scam.
So, these new icons, they spent money to make them and all that. They won't just give them away for free, no, they're going to make you pay for it. Now, if this were a P2P game, you'd get them for free, but not in an F2P game, sadly.