Did I say I wasn't enjoying it? Don't assume my enjoyment. I just feel like the lack of humans is a mayor plothole or that I missed something important.
In the intro it explains some tragedies or events. Humans are underpopulated due to the wars and pollution that have ravaged the world. Humanity was on its way to stabilizing into positive growth after them. Then the portal incident happened and now you have monster species pouring from every which wherever and they far outnumber the native sapient population species(humans) due to the ease of travel via portals to the hub that has formed on the human world due to the two gods having fought their battle there. The majority of humans aren't even situated where most of the game plays out, the most that are close enough to be a factor being in the army of the king.
Monsters breed enourmously fast too, while humans as far as I know still undergo the usual 9 months so it's understandable why the other species would outnumber humans quite quickly. Another reason for the monster population growth is that while it is free to go through the portal to the hub, it currently costs money to use them to go back or away from the hub which is a deterrent for the people who came through them to go back. It's like tourism with little to no reason to go back, essentially immigration. The portals aren't stable either and close a short while after opening so they can't go back unless they want to face unknown wilderness, so most stay due to having either no choice or it would be better for them to not go.
Even so, there are many human NPCs that you can interact with. The portal guild girl for one, then there's the soldier woman that occasionally appears in the river, the king, the prince, and every human combatant character that you make a token of. You can also get human characters to interact with as part of the king's quests, either for sexual or combat training. If I remember correctly there's a way to "recruit" human character enemies but it involves using lust and some abilities that I think is only available to species that are part of the "succubus" family. I might be wrong on the recruiting part but I do remember being able to do something like that.
TL;DR: The game plays out after a war that affected humans and a battle between two gods, most of the game being near and around a portal hub that is connected to various worlds where the native population isn't humans and allows free travel from their locations but you have to pay to go back. Of course there isn't going to be a lot of humans.
Sorry for the long post, just wanted to give an opinionated explanation that may have varying levels of accuracy. I don't have anything personal against anyone here, so don't take this as a direct response.