Forrest Wickman writes: 

If you’re among the millions who have spent a significant portion of the past month watching videos of goats yelling like humans, you may have wondered: Why do goats yell like that? Are they distressed? Do they yell for any particular reason? Are they trying to tell us something?

Good question.

It turns out that goats yell for many reasons.

Yelling, for goats, is not unusual. They will yell for all sorts of reasons. “Mother goats call for their young when they get separated,” explained goat specialist Dr. Daniel Waldron of Texas A&M, and “young kid goats also call for their mothers.” “Goats may also ‘yell’ when they expect to get fed,” continued Dr. Waldron. “If I feed one pen of goats, the second pen may start ‘yelling’ because they want to be fed right now.”Dr. Jean-Marie Luginbuhl of North Carolina State, a specialist in meat goats, agreed. “In my experience with goats, it does not take much for them to scream bloody murder, as if you are torturing them, when simply handling them.”

And why do they sound so much like humans? It’s a bit of a mystery, apparently. But the first thing to realize is that not all goats do sound like humans. Instead, they each have “distinctive voices,” Dr. Luginbuhl explained. While some individual goats may yell like humans, others have different voices and may not sound like humans at all.

Basically, it's what they do.