Thank you for this explanation. It makes sense, but I don't really understand why it has become so popular.

Professionally, my experience is that certain software components need to run together on an individual machine (e.g. database server, app server, web server), and then those machines need to be networked in a certain way (e.g. web server talks to app server, which talks to database server), so I really need to care about the architecture of individual machines. You can then scale this out horizontally (e.g. add another web server) or vertically (e.g. upgrade your database server).

I'm old, so maybe I'm out of date, but having a cluster of "compute" that I can run arbitrary workloads on sounds neat, but is a capability that I've never needed.