But honestly I'm not sure there is much of a line between the two. I've seen microservices that just return True/False and ones that return 100 lines of json, which are arguably more web-services than microservices.
I honestly think it's a distinction without meaning.
A CLI not a service: there is no operational complexity to "keep things running" in a CLI: you just chain some things together with pipes and that's that. The nice thing about that is that the text interface is generic and you can do things the original authors never thought of. With microservices this usually isn't the case and things are extremely specific. This is also why "do one thing and do it well" doesn't really carry over very well to GUIs.
A lot of microservices I've seen are just functions calls, but with the extra steps of the network stack, gRPC, etc. Some would argue that this is "doing microservices wrong" – and I'd agree – but the reality of the matter is that this is how most people are actually using microservices, and that this is what microservices mean to many people today.
Instead of "microservices" we need to think about "event-driven logic", or something like that. Currently the industry is absolutely obsessed with how you run things, rather than how you design things.