I get the idea behind it. It's supposed to be something like, "Oh I love this game, and support it" And riot's return is, hey, here's a little something special. The problem is it feels super duper money grubby, and more like, "Haha you can't get this if you don't pay" more then, here's a gift for those who were investing time and money into our game.
I feel like the better way to really introduce prestige skins would be along the lines of 1 or two per year, and the top 10% of people who dumped the most money in the game would get it as a gift, or a thank you from riot.
Maybe I'm interpreting this 100% wrong, and maybe it is just a money grab, but I don't feel like that's entirely the case. You have to notice, the capsules that come with prestige tokens cost 750 rp - the same cost that capsules have cost in all events. In other words, while the prestiege skin serves as an incentive to buy more, it is not, however, something that in itself costs money. It's a Bonus.
I don't know, I just don't like hating on a group due to an interpretation, seeing that there are so many other possibilities behind the rational.
While you might say, oh it costs 140$ to get it, I don't find that quite true. To be honest, I'd buy the capsules regardless of prestige, to me, the skin at 140$ is more of a cherry on top, being that I find the capsules worth it in the first place. To each their own however.