there are around 40+ Legend affixes, maybe 50+? about a third of them can’t be rolled with Ruby. when using Ruby, you are given 6 random choices to choose from, so if you aren’t lucky on your first roll, it might take a few Ruby’s to get the affix you want.
I have gotten the Legend affix I wanted on the first roll, in the first 5 rolls, and rolled 30 times without getting my Affix and running out of Ruby’s.
here is a good post on affixes you can’t get, or have to meet certain conditions to get. hope it helps.