A service small enough that a team or engineer can rewrite it in a cycle/sprint.
When it’s bigger than that, you have the compounding effects of other systems that interact with each other.
"Why are there so many small services running? Surely we can shut down / delete/ merge together a bunch of them to clean things up"
I'm pretty sure Elon has also hit this fallacy during his tenure at Twitter.
It’s such a Weird fallacy since I feel like the entire point of Microservces is that there’s an inherit reason they’re microservices in the first place.
If you don’t know why, you investigate why. It feels far easier to make a monolith than a microservice.