Whyso? At work you're expected to function as a team, and part of being a team necessarily means needing to make personal compromises for the team's sake.
In this situation, non-native English speakers are going through the monumental effort of both learning English and having to put their skills to the test every day instead of them working and communicating in their fluent language. While people with accents such that they're harder for non-native speakers to understand are being asked to have clearer enunciation - for the sake of the team.
You're not being asked to change your accent, just to have clearer enunciation (if your org's DEI team said "accent" instead of "enunciation" then their wording is unhelpfully vague or demonstrably open to misinterpretation) - and not for the benefit of people who aren't themselves doing anything for their own situation (it's not like the non-native English speakers in your workplace are insisting everyone speak their language, after all). Everyone is making a compromise for everyone's sake. There's nothing ironic about it at all - just unfortunate messaging from the DEI people.
The irony is the reduction in diversity of speaking is requested to improve the equity and inclusivity of comprehension.
I am more inclined to charitably view it as a minor inconsiderate overstep, an internal matter not for public consumption. Perhaps if it was phrased as 'enunciation' it would not have garnered any reaction.
There is no way to do what you suggest without risking a mob.
You should risk the mob. It's not ok for a DEI team to ask people to tailor their regional accents for foreigners who don't speak english well. You can also release this anonymously (it's hard for people to deny written exchanges because the results are in many inboxes).
Also on a point of misunderstanding it's not an Americans vs. Foreigners situation.