Just saying, the people you are making skins for, like Ahri and Gangplank already have like 4-5 good looking skins. Whereas some champions only have 1 or 2 that are lazily designed.
has 1 skin that just recolors his purple, wheres 
has tons of skins that look different from each other.
Making skins for the champions that have a bunch isn't bad, but all I'm asking is to make skins for the champions with just 1 or 2.
Give it time. Zac is actually quite new, so you shouldn't be surprised that he only has that one skin. Thresh, who was released two months before, has one more skin compared to Zac, and it is very recent (Championship).
Annie is part of the release champions; she's been in the game since the very beginning. It is to be expected that she has more skins.
It will come, just wait for it... Older champions get more skins! Also, champions that aren't played very much won't get many skins, since the skin wouldn't sell. I'm not saying it's Zac's case, but it's Poppy's case for example.
The reason why skins are so few is that the amount of time to create a Skin that is both "cool" and Unique is more than before.
Zac is hard to make into an alternate that is not just a color rework as evidenced by his purple ooze variant.
