The problem is that they are microservices in name only. Where a unix utility does a few hundred or a thousand lines of C code for its entirety, a microservice will depend on a complex software stack with a web server, an interpreter, an interface with a database, and so on.

It's easy to forget this complexity, but it comes at a cost in terms of performance and, above all, technical debt. The microservice will probably have to be rewritten in 5 years' time because the software stack will be obsolete. Whereas some unix utilities are over 40 years old.