Whole point of DLP tools is to lock in and control data, but not in the way you are proposing. And also it's not increasingly being used that this manner way, but that's the entire point with these tools have been around for decades for SharePoint and local file servers. The policies are set a platform level rather than stored in the file.
So organizations can just turn off their Purview policies anytime they want and if they switch platforms. And of course during a migration they'd need to deal with organization policies, including coming up with policies on the new platform like G Suite which also has DLP.
But the tools are also have some pretty non-nefarious business cases like not letting somebody in finance copy/paste or screenshot to skim Credit Card numbers or not letting Word docs with stored in the XYZ super secret health information folder be emailed outside of the organization. So LibreOffice not being able to block your SSN number from being leaked or unable to prevent a government official from editing/delete documents on legal hold may be good things in your mind. But the downside to those tools is they do lock you into the walled garden of tools that can enforce those policies when the organization has those policies. But it's not being permanently trapped, an organization can migrate to another walled garden with DLP tooling or migrate to open tooling as they please. But if they needed DLP in the first place, they probably can't switch because the open tooling can't do what's needed, but because of some conspiracy in wanting to vendor lock-in.
