Obviating communication costs within teams is one thing, but what of the overhead and costs of communication for the whole system? Eg. how do you avoid the cost of deploying a new team that ends up deploying a duplicate microservice?
You may also explicitly establish an architecture team that has oversight and tries to ensure everyone's aligned on direction. But mostly if you at least have some shared place where you explicitly communicate the creation of new services or design development then it allows you to avoid some of the issues you're talking about. The other thing is having a way to discover APIs and services so you can go check if something exists before building it. In many cases teams do still build a variant themselves because they need something slightly different and thats ok if they're willing to support it.
It’s not perfect, but it’s a lot more efficient than the previous state of every individual developer needing awareness of what every other individual developer is working on at any given moment.