First, you can run proprietary software on free software. So, running free software does not preclude license monitoring. It is also possible that certain licenses are not allowed even if they are approved by the FSF or OSI.

The goal more broadly is enforcing corporate policies around risk or whatever else needs to be enforced.

It may be that you HAVE to use certain kinds of software ( VPN was mentioned ). Perhaps you are NOT allowed to use certain software on work computers ( torrents and Steam clients come to mind ) or visit some kinds of websites.

The other risk that a company may want to monitor is ensuring software is up to date ( open source or not ). Stale software can have vulnerabilities that become attack vectors for the bad guys.

Finally there is access control, privileged access, and auditing. There may be systems or data that employees are not allowed to access or are only allowed to access under certain conditions.

I am not advocating anything here but it is totally normal for corporate IT to be tasked with limiting corporate risk and creating an auditable history of compliance. These are the kinds of tools and policies they use.