A lot of infrastructure choices will be dependent on the stack you use and the scale you need, so it's not a one-size-fits-all. I simply wanted Airflow since it fit into my stack neatly and was open-source and portable so it wouldn't lock us into AWS as I could stand it up anywhere else super easy because it was containerized, along with the rest of our workflows. Also when I looked at ECS it seemed better for workloads where there are many short-lived containers with varying hardware needs (CPU vs memory) or to get cost savings for workloads that could be delayed to run on spot prices. But for long-lived services where containers were running 24/7/365 like Airflow, GitLab, or other services, ECS ended up being more expensive than just getting a dedicated EC2 host running Docker.