>>532059824
Ingrid is a character they can potentially sell merchandize of, license or use in future games.
Lucy is an advertisement for someone else's franchise. It's why Bandai put Akuma in T7, but Capcom didn't put a single Tekken shitter in the SF5 roaster.
Don't get me wrong I'd love to play as Nazuna or some other flavor-of-the-month anime character, but Street Fighter is too big for those hobos.
They have a special relationship with SNK, so it doesn't count.