The devil is often described as having goat legs and goat horns, sometimes with a head and a human body. How did this come about? Why the goat particularly? Why not something more ferocious and well, devil-like?
Have you ever lived nearby goats? The pests are a pain to deal with and will get agrresive for no strong reason. They would thow you into the sun just for looking at them wrong.
Jokes aside goat imagery being related to Satanism and devil-worship is a really modern. I guess your comment comes from the Baphomet imagery being almost universal in modern media depictions of the fiery underworld. The first instances of Baphomet portrayals comes from the late 19th century and it is usually attributed to the book "La Clef de la Magie Noire" published in 1897. The reason why its specifically a hermaphroditic half-goat, half-man is because the artist specifically wanted to allude to pagan idols, which share animalistic features and a perversion of God's creation by rejecting his binary commands and order. There isnt a specific reason on why it was a goat and not another animal.
This symbol later was adopted by many prominent occult groups and satanic worship which catapulted its popularity and its image in the public to be immediatly recognized as a satanic figure. Most prominent of those users was Aleister Crowley, whicb added a layer of mystique and pseudo-history to it.
As for the actual origins of Baphomet as a name or deity? Like the imagery associated with it today its also relatively modern(11th century, which is quite new compared to the supposed pagan idols it is referenced to) and its also a big made-up fiction, as it was a fictional idol which the Templars were accused of worshipping (which in itself is just a corruption of the name Mohammed, since Christians at the time thought Muslims worshipped Mohammed as a God on its own, and the Templars were accused of fraternizing and adopting islamic teachings).
So, very funnily, the goat imagery is basically a thousand year meme based on perversion of facts which keeps evolving and gets stuck in the popular memory every now and then in several of its iterations.
For a good read on the Templar trials and Baphomet accusations "The Templars and their myth" by Peter Partner is a good read, alongside the newer "The new knighthood" by Malcolm Barber.
As for the use of the goat imagery in Satanism I can reccomend "Satanism:A social history" by Massimo Introvigne.