It's not that they aren't equal, it's that they simply haven't reached the point in the story where it makes sense to give them anything like that yet. Nobody is being ignored, but the story has to build to a certain point where they would accept such a thing being done to them. This is not like most games on here, where that kind of content is thrown around freely, the story is the top priority here.
The three MILFs are Haruka, Sara, and Maki, though there's also Tsubasa (Touka and Tsukasa's mother), Osako (karate instructor found in Ayane events), and Wakana (another teacher found in some events at the bar and school) as well. Not sure who Miko is, there is no character by that name, closest I can think of there is Miku and Makoto, but you specifically asked about Miku and mentioned Makoto, so they can't be this Miko.