What's holding Riot back from creating more chromas?

Hey, as someone who really likes the concept of chromas (I really adore as example Zacs, Caitlyns, and the upcoming Braum chromas), I am kinda wondering why we don't see more of them in each patch. I was kinda hoping to see more champions getting chroma packs in like every PBE cycle update, but it seems like its kinda.. slowing down. It's good to see new skins with new particles and such in every patch too (totally hyped for Elementalist Lux), but.. I just wonder what's keeping them down to make more chromas lately.

There are alot of base skins with chroma potential (Sona, Twitch, Amumu, etc.) as most of their base skin covers one certain color, recoloring that certain color would defenitely please alot of their player fanbase, as I've seen with Zacs chroma pack. There was also a interesting thread of a Heartseeker Orianna chroma concept, and I really adored that one as well.

but yeah, out of curiousity, what does Riot holding back from creating those more frequently? The Skin team? Popularity? the backlash of Chromas in general?