When your application is small and simple: If your application has only a few components and does not require a high degree of scalability or availability, then using microservices might be overkill. When your organization does not have the necessary expertise: Building and maintaining a microservices architecture requires a high degree of expertise in areas such as distributed systems, API design, and containerization. 

Also If you don’t have a team size that cannot handle the microservice workloads, this will only result in the delay of delivery. 

https://www.fpt-intellinet.com/intelliblog/three-reasons-why-not-to-do-microservices