When is an API Gateway not worth the operational overhead?

We've all seen systems that do well with an API Gateway for things like authentication, rate limiting, and request routing. It's a standard way to do things with microservices, sure. But I'm curious about the other side: when does an API Gateway make things *too* complicated? For smaller teams or simpler setups, sometimes just talking directly from service to service, or even using a load balancer for basic routing, seems like enough. Are there specific team sizes, how many services you have, or traffic patterns where an API Gateway just adds too much work for not enough gain?