Two major forces behind the rise of distributed systems like microservices are:

Cloud computing

Cloud providers now provide everything on-demand. Serverless and Lambda functions have become very popular among organizations to scale fast.

Containerization

Containerization technologies like Docker and Kubernetes make it very easy to spin up new services and scale them on-demand.

Observability is a term from control theory, which states that a system is observable if the internal states of the system can be determined by examining its output.

https://signoz.io/blog/microservices-observability-with-distributed-tracing/