Why don’t we drink other animals’ milk?

Not legit. Insulin can't be ingested, it doesn't survive the stomach. So while it may contain a ton of insulin, it's broken down long before it's of any use to anyone. So either you make it yourself with a functional pancreas or you inject it.

“What we've discovered,” says Lee, “uh, what we've concluded, you know, is basically that the machine that would fit a pig's teat is a human breast pump. It fits perfectly.”

Too bad they did not describe what pig's milk is like, or how “Anyone who farms pigs would say that pigs' milk would make an incredible cheese,” How would an ordinary farmer know, having never collected the milk?