We use ES and Kibana open source. Our entire infrastructure is on AWS and if AWS is managing the installation and maintenance efforts thats a great help.
ES was never going to make a penny from us anyways and AWS is not making any money from the ES software itself. What they are making money is from our usage of their core services. Same goes for all the other open softwares, Kafka, Airflow, EMR to name some. Plus it would be dumb to have your infrastructure on AWS and buying ES cloud service where you'd require to send your data out of AWS as you'd have to pay for the data out.