It's milk that the company has extracted all the nutrients from, and replaced them with sugar. Now you get expensive sugar water, and they can sell the good stuff in other products such as whipped cream, heavy cream, and butter.
Edit: apparently the higher sugar content in skim and nonfat milk is because the removal of fat concentrates the remaining lactose. They don't add additional sugar. The original point still remains though, that it's mostly just milk flavored sugar water.
The answer above that called the other 98% "mystery fun" was far more informative than this fabrication.
Pasteurization is a very, very important process for keeping humans safe. Nobody should be framing it as "extracting the nutrients". This is especially true right now in the US, since dairy cows in multiple states have tested positive for bird flu. Their milk has been confirmed to have the virus in it, but it's dead virus thanks to Pasteurization.
I'm not talking about pasteurization. Whole, skim, and nonfat milk can all be pasteurized. I'm talking about them taking all of the nutritious natural fats out of the milk and replacing it with sugar to make skim and nonfat milk.
I don't disagree with your conclusion, but I don't think they replace anything with sugar. Milk is just high in sugars, because it's supposed to give energy and nutrients to a growing calf. If you remove the fats then the sugar content is higher as a percentage.
Milk isn't all that healthy in general though. It's liquid for a calf to grow. It's much better to drink something made for human consumption and dietary needs.
Ah, you are correct. I just checked. I always thought that they added extra sugar so that it doesn't taste terrible. I know they do that with some other non-fat foods. The higher sugar content in skim and nonfat milk is because the removal of fat concentrates the remaining lactose, like you said. Thanks for correcting me!