The systemic racism people are going to go wild about this
This would directly penalize endangered languages and dialects, which is a tragic loss for linguistic diversity. I think a lot of people hoped the WWW would connect these small and dwindling communities, and even help revitalize them, but policies like this sound actively harmful.
If we're looking at it through the lens of systemic racism, it seems pretty straightforward as well – anyone who speaks a non-standard variant or dialect of their language will have less power to share their thoughts and ideas. They will also see less other people doing so, creating a feedback-loop discouraging the use of non-standard language.
If a recipient doesn't speak the language, the speaker doesn't have much power in the first place. This is noise reduction.
I think ignorance is a fair answer for an individual like you and me.
However when you are a giant organisation, the organisation can be evil without anyone individually being so. In organisation ignorance and evilness is really hard to distinguish, and easy to conflate on purpose.
It is the job of the leadership to not be ignorant, or at least to hire someone who isn't.
Thats why AI ethocs teams where the correct move.
https://www.linguisticsociety.org/resource/multilingualism
Of course in the US this is not the case, and Twitter is a US based company that creates software used globally.