Human milk IS designed for human babies, because it contains the right amount of fats and nutrients needed for growth of the body and especially the nervous system of a baby, but it would be silly at some point to continue consuming it (and it seems to be that the documented cases of women breastfeeding nine year olds is more or less a psychological thing than an actual need of the child anyway). After the initial growth stages are passed the physical need to strengthen and grow a young body to maturity lend itself to many foods.
Milk is an easy one for kids, they will suck the jug or carton dry in many cases when they like it and you can add vitamins and minerals while reducing the fat content easily as well. While doing this the remainder often lends itself to a myriad of other foods that can be created with it. While I will not argue with you one bit about the need for vegetables to add vitamins, minerals and overall needed diversity to the body's processes it is pretty clear that milk is extremely useful, if not actually perfect.
You gotta advertise, it's a slogan, "the perfect food". And you need plenty of food 'ammo' when you have fussy young eaters to train.
Just no 'mucus'. Save that for Slime...I am too old to have ever been into Slime.
PS People actually eat octopus and squid...I save that for orcas.