DEI statements are important because they show individual awareness of historical inequities and current biases that form modern society.
In an organization that wishes to promote more equitable outcomes for society and its employees, ensuring that existing/prospective employees are aware of biases that might color their own judgement is useful in counterbalancing them.
As a consequence, a DEI statement at the time of hiring or promotion is useful in encouraging self-reflection and promoting DEI.
... that said, from a personal perspective (and with apologies to anyone working in HR), they seem like the typical "moderately good idea that's run through the HR cost center grist mill and comes out as the most unimaginative, milquetoast check box possible" implementation.