It's called marketing. It's a new product so you need to help the consumers understand what it is similar to it and it's use is similar to milk which you put inside cereals.
If you don't do that you would have to invent a new word. I mean what word could they use? Your sales would not be as high.
You can't use juice because it's not a juice. Juice is fruits. Is there a name for plant or seed juice?
If it was me I would use "flow" because it's liquid and it flows.
Almond flow, rice flow, soy flow,
But even so. Your sales wouldn't be as high as milk. Calling it milk allows the customer to quickly know that it supposed to be used the same way you use milk.