Stop making threads asking for champs to get skins, and
Start making threads asking people to buy the existing skins for that champion. That's how you get new skins made. If people are gonna continue to buy Yasuo skins and not Vel'koz skins, then Riot's going to continue to make Yasuo skins. They're going to use the people they pay to make skins to make skins that will make the company money.
So if you can get people to show that skins for that champion make money, they'll do it. You're not going to get anywhere with just the backing of a less-popular champion's reddit community.
and
since they only have one skin (worlds not included + limited availability) because you are limited to one skin. Because champs like
have an insane amount of skins the number of skins to be purchased is way higher, so when riot looks at the stats, they will be seeing a higher number for lux than champs w/o that much