It's also possible to run Caddy in Docker as non-root, but it requires jumping through some hoops when configuring Caddy, for example changing the HTTP and HTTPS ports in global configuration to something else, since those ports are necessary to use for ACME.

If the official Docker image did that, then most users would be very confused and we would get lots of support complaints. A cost-benefit analysis told us it was not worth the headache to run as non-root since the Caddy project values highly user experience.