Lieges usually aren't too clear about how many knights they absolutely need. Some like to have a lot too, even if the region really doesn't need it.
And for dukes of large cities, yeah, took me a while to get some of them to give me above 10%. Now I just go straight for the 10% for a huge city, way more if I know the duke needs knights.
But even so, some places really can't be helped.
