Because it's overly long for a joke that we get from the forst minute, and because it misses the point (you can't make a drink out of a tree, but you can out of some plants) ?
I don't consume soja "milk" or various vegetal versions of animal-produced aliments, and I find their naming silly (okay they are supposed to taste like these other things, but it still sounds odd). And yet, I find this commercial perfectly stupid and trying way too hard to be funny. Even as a comedy sketch, it would be a bit of a failure. As a commercial, with an actual message ? Pathetic.
(Also, even as a ravenous devourer of flesh and cow milk drinker, I do appreciate the ecological rationale and intent behind alternatives, so making it a side-vs-side "fight" for the milk industry and against these alternatives would feel really nasty. If people enjoy more than I do the taste and idea of, like, "soy milk" or whatever, all the better for them and the planet. Trying to deride them and push them to cow milk consumption, especially on the behalf of an industry's profit -advertisement- is beyond lame, ideologically. Now if these alternatives raise other actual concerns, they should be criticized on these genuine grounds. Not some braindead "you wouldn't milk a stone, lolol".)