The binary is not statically linked (has not all the necessary libraries). If you want the Elastic Agent in an Alpine based Docker image, you will have to compile the binary yourself.
I suggest strongly to use the official image docker.elastic.co/beats/elastic-agent:7.13.1.
Please use the Elastic Stack > Beats space for Elastic Agent related questions. This space is dedicated to discuss about Elastic Cloud on Kubernetes (ECK).