How on earth has it become an ideological project that is associated with limiting language, confining thought, forbidding discussion, and restricting evidence to a procrustean bed.
In the long term, form follows function. If something isn't good at its function it has to adapt. So anything that is long-term successful must, by elimination, have a form well-suited to its function.
In the short term, function follows form. Given a set of rules or incentives, behaviour inevitably follows - favouring short-term advantage. If that short-term advantaged behaviour is not consistent with long-term survival, the form may not survive.
In this case, the form of "DEI" is a middle-management/NGO-type layer that gets to tell everyone else what they're doing wrong. And that "tell everyone else what they're doing wrong" is the key feature. Of course that is going to attract a very particular sort of personality and lead inevitably to purity spirals as they police each other. Regardless of what the original intent was.
James Lindsay has a saying "the Woke slope is always slippery". Basically, they can't leave anything on the table. If someone doesn't declare something as problematic, someone else will, and they will then claim they're better than the people who didn't say it was problematic.
Another way to put this is that Wokeness (or, the various Theories of Critical Social Justice) has no brakes. There’s nothing to stop a Woke train once it starts running. The reasons are not bugs of the Theoretical worldview but are, in fact, features of how Theory operates methodologically. All the way back to Hegel, any idea that could still be hit with the dialectic must be hit with the dialectic; any problematic that isn’t critiqued leaves the status quo intact; any social construction that isn’t deconstructed maintains the possibility for oppressive systems of power.
This particular form is effectively a virus or cancer - it's great for its participants, but the surrounding society can't really survive it. It has to be contained.