Q: "Alpine has NO benchmarks or specific profiles to scan the Alpine Docker image"
A. Right, that the case because of the design of the distribution.
Q: "Does someone know why it is? Why are none of them supporting Alpine hardening?"
A: Because it is a Linux distribution built around musl libc and BusyBox for Power Users, smaller and with more security in mind.
You'll probably need to "ask other questions" regarding Alpine Linux compliance, means in example like Hardening: the Apache Alpine Docker Container. And that's why some own work might be necessary