[2023] Why won't riot make legendary skin for every champion, then care about secons legendary?

What I want to say is That I don't really understand why many champions (ex. Cassio, syndra, lissandra, rengar and many others) don't have legendary skin atm. I know that many champions can't fit to a certain theme (ex. Gwen with her scissors) but why on earth can't they just make a skin that is fitting this specific champion and then add champions that also fit. It's just really sad and something I wanted to point out.