AWS Lambda requires a specific RUNTIME to act as a broker between the hosted container apps and the Lambda service. Why doesn't Google Cloud Run require such a runtime? What are the pros/cons and technological implications of that?
They're two different products. Lambda would be similar to Cloud Functions, and you would need to specify a runtime.
Cloud Run, on the other hand, is more like ECS Fargate. It runs containers, so in a sense your runtime would be whatever your container is running whether it be Python or NodeJS, etc.