Because that wasn't my point at all. I'm all for an all-female skin line myself, as long as the concept's great enough.
Infernal Nasus is a concept that appeals to the majority of the playerbase: dudes. What do dudes prefer? Nasus turned into Cerberus(if you don't know who Cerberus is just google the name). Since that appeals to the demographic they are targeting that's the place they'll be investing upon, in order to make profit, because they are a company. Artistic vision and/or integrity is irrelevant, because they are above all a company, and a company needs capital.
Dandelion sniffing Soraka, albeit a concept intruiging, is not something that would appeal to such an extend as Infernal Nasus, thus it takes lower priority and more iteration than normal, because in order to make profit off something that's got lower appeal, you've got to think this through, otherwise you're wasting your resources when you could be investing on something that's guaranteed its profit. Order of the Lotus is proving so far to be a female skin line, Ionia targeted at that. Star Guardian Lux, a skin for a female champion; obviously girly(not gay, not feminine). Obviously targeted to those who wanted something more playfull, colorfull, girly, with a hint of anime refference in there if possible. They gave it to us. Targeted to the demographic that will make profit off. People like me, will not buy the skin, allthough we might not dislike it, aestheticaly for us it might be too girly to use. It's not about whether I like it or not; I quite like it as a concept, but I don't have it because it's not my type. It's not by any means ugly, but it doesn't appeal to me the same way Cerberus does. That's not the same for other people though, and they will buy it, and that's good because it gives profit.
Since this concept appeals more to you, they will create it, and give you the skin. Then you'll be able to play the hell out of Dandelion sniffing Soraka. But it's not because there are skins of some other type that this particular concept got materialized. It's not because there are far too many hardcore skins that there's a need for dandelions. It's because that's what they wanted to work on. Star Guardian Lux, came to be not because there were too many fem-fatale skins in the game, but because Riot decided Lux had too many militarystic/feminine skins for her, so they wanted to create something colorfull, girly, playfull and vibrant.
I never said an all-girl team skin set should't exist. What I don't want to exist is such a skin line created from spite towards the rest of concepts in the game. An all-girl team skin set should be created when the right concept comes into being, not because the vast amount of "bro" skins exist. Not because of some spite. So what about the "bro" line? It's a concept that could potentialy be great, entertaining and unique, a concept that could appeal to anyone with a sense of humor, with anyone that looks for something more lighthearted without it being childish, hardcore, mythical, high-tech or whatever. A new popstar skin will come out when the concept is right, not because Omega Squad Teemo came out and gave us another hardcore skin that turned a fluffy satan into a black-ops specialist reconnaissance PTSD asskicker(with tons of Call of Duty refference) and all of a sudden the game took a turn in favor for the dudes.
"Bro" skins and whatnot, take shorter time to iterate because their concepts are already partialy established. Look at Gragas, he's fat, drunk 24/7, he has a sort temper, he says stuff like "I'll drink you under the table scrub" and "only time I have a drinking problem is when I spill it, eheh". What does he need to be a "bro"? A steroytypical beer barrel with tap, flipflops, a tank top with a bunch of stains on it from spilt beer, worn-out jeans and perhaps a jockey pointing backwards or something. Give him a funny VO ala-Brolaf and you're set. How does one creat Dandelion sniffing Soraka? Soraka's a being that came from the stars and she aids those in need. She's freaking purple, her legs are made up of goat and are pointing backwards from the knee down, she has hooves and a yellow horn sticking out of her head, which has elven ears at that. If that wasn't enough, she fires banana-like projectiles from her magic staff, and she even makes banana jokes herself. How are they going to create a Dandelion sniffing Soraka from that base, without it looking like Celestine Soraka, with it being unique, with a concept that fits into the game's requirements and aesthetics? Bro-Gragas just needs his barrel turned into a beer barrel, how will Soraka's stuff resemble her sniffing dandelions?