I suspect the plant-based "milk" makers are investing a lot of marketing resources in smearing the reputation of milk as unhealthy, just like the margarine makers did before to promote the replacement of butter with cheaper hydrogenated vegetable oils.

Milk has minerals like potassium and a low glycemic index as lactose takes a while to digest. That could help.

> I usually see people calling milk unhealthy

Usually with zero actual supporting data

Somethings are simply bad for you, without qualification, but for the most part it only makes sense to use "healthy" or "unhealthy" to describe a diet, not individual foods.

Milk has lots of protein, minerals, and fat. Whether that's good or bad depends on how much of those you're getting from other sources.