Champions That Haven't Been Touched By The Skins Department

Riot has recently given us a preview of their upcoming Star Guardian skins for Ezreal, Ahri, Soroka, Syndra, and Miss Fortune before they are put into the PBE for testing. Now, I really like these skins and I am one of the many suckers who are drawn to things that look anime. But, I have grown quite frustrated with Riot for focusing their attention and effort on making skins for certain champions that seem to be easily compatible with most skin design concepts. I imagine Riot makes their skins based on how a concept could work with a champion. But it's 2017 and there are certain champions that don't seem to be have been touched by Riot since their last skin they were given. Champions like Rengar, Cassiopeia, Rumble, Irelia, etc haven't gotten any new skins in a long time. For Rengar his last skin was made back in 2013 or 2014 and the same would go for Irelia as well in between that timeline with Rengar or maybe some where near that. Cassiopeia and Rumble are champions that have been around for a long time and Rumble's skin was given before the Summoners Right update and I don't even remember when Cass was given her last skin as the splash art of her skins appear to be outdated compared to most. It's just I wonder if Riot has made any effort into revisiting these champs in the skin department for these past years. I realise they have their priorities and I just thought they would frequently revisit champs that haven't been given any skins for a long time. This isn't a rant but I just wanna express my frustration and concerns to the LoL community and to know if I am the only one who thinks like this. <3

Feel free to correct, elaborate, and/or explain to me.