Executives at Target made the calculation that their sales wouldn't decline much (if at all) by publicly canceling their DEI programs.
To the question about Target and Costco's prices: Typically these retailers will have price matching policies in place to keep foot traffic.
Quick google search implies (not sure how accurate this is), that approximately 12% of Target's demographic is black [0]. Seeing close to a 10% drop in foot traffic for a low margin business like Target when a competitor is seeing almost the near opposite gains is a signal someone really screwed up.