There would be the same reaction if FB or Instagram or any other big platform was found to be allowing ads next to objectionable content (content the company in the ads would not want associated with their brand) AND that platform said that it wasn’t an issue, they won’t change policies to prevent it, and told them to go fuck themselves.
Twitter could absolutely have filters in place to prevent ads from showing up next to literal Nazi posts with a simple word list. The posts Media Matters showed were not subtle or underhanded, they were saying the quiet parts out loud. It would be trivial to prevent ads entirely from those posts, but then they’d lose ad space. It would mean less if this had happened with borderline posts or posts using coded language.