Only two skins?!?!

So I buy some Riot Points with money I got for my birthday and hop on League to buy a skin for my main, Poppy. I look at the available options and am disgusted to find out that only two skins out of a supposed six are available. At first I think this is just some dumb thing but I check other champions skins to find they are all intact and buy-able with the exception of some very old skins begging for updates and are probably in the process of being patched. Because all of Poppy's skins are legit for season 6, why are there only two skins that I can buy? I just know there's some blatantly obvious reason that I'll feel stupid for overlooking, but please tell me why!

By the way, the only two available are Battle Regalia Poppy and Scarlet Hammer Poppy, if that helps.