The argument there is that people from under-represented populations have to face discrimination regardless of their economic status. This is why DEI looks at the whole cross section of
socio-economic status, and not just the economic part.
To put it simply, a poor white student from rural Alabama only needs a proper accent and a good suit to blend in with the upper-classes. However, a black student only needs to lose access to their parents money and they immediately have a longer harder uphill battle to fight against racism which will presume them to be uneducated, underperforming, and generationally poor unless they work 2x as hard to prove it wrong.
That said...
I do think there's a danger in supporting DEI programs simply because they have good outcomes (which other posters are doing). If a group achieves your end-results but doesn't have your philosophy, then my life experience (e.g. MAGA) has shown that they will become the enemy that you don't see until it's too late.