Buffalo, goat, and camel milk are all also pretty commonly consumed. Source: I’m severely allergic to cow milk protein but I’m able to enjoy milk products from various other animals.

>Also isn’t it curious that humans are the only species to drink another species milk?

It's not that surprising. If you want to drink another species' milk, you have to be able to domesticate that animal. Sure, you get ants doing something vaguely similar with aphids, but when talking about mammals no other species has the capability to manage it, so they just don't have the option. At least, unless they have humans around to provide it for them. If you had a dozen intelligent mammals with civilizations similar to humans, I bet many of them would be milk drinkers. It's incredibly useful if you are a pastoralist, since it means you can get calories out of your cattle or goats without having to kill them. Useful enough that the descendants of most pastoralists still bear the genetic stamp of heavy selection in favor of milk drinking (aka, lactose tolerance into adulthood).

> And why not dog milk- or rat milk?

Obviously you are joking, but it's all about diet and volume. The whole point of dairy, from a premodern perspective, is turning grass into useful calories. Dogs don't produce a lot of milk and you can't graze them, while rats are far too small to produce usable volumes of milk.

That said, Simpsons did it

They do goats and sheep and some wierdos even horse but cows are just the best at it. It's also weird that they have 4 teats but typically only have one calf. That's not usually how it goes with mammals. Sheep, horses, and... goats? I can't remember if it's the same with goats... but they've all just got two. And goats and sheep are often bred for twinning. So wtf going on with cows and their super mammaries.