“Microservices” was, IIRC, more about rejecting that and returning to the foundations of SOA than anything else. The original description was each would support a single business domain (sometimes described “business function”, and this may be part of the problem, because in some later descriptions, perhaps through a version of the telephone game, this got shortened to “function” and without understanding the original context...)
It's a (human) scaling technique for large organizations. When you have thousands of developers they can't possibly keep in communication with each other. You have to draw a line between them. So, we draw the line the same way we do at the global scale.
Conway's Law, as usual.
The name was properly chosen poorly and led to many confusions.