Why can't I access all commands in recovery mode?
The recovery partition is a bare-bones version of macOS which can be used as for various things, such as installing macOS again or disable SIP (system integrity protection). To keep the recovery partition small, Apple decided to not include all CLI tools that are available in macOS.

For security reasons, not every user is able to access all files. The root user should be able to access all files and run all programs. It's a permission issue. However, he's not able to run programs that don't even exist on the recovery partition, so changing the user to root won't help you.

If you do want to use those programs, you shouldn't be using the recovery partition anyways but boot a standard macOS partition.