The original page's html tags have been stripped, but were replaced with whitespace. This results in contents that are difficult to read and/or shorten in any easy way. Ideally, MathML contents would be shortened to a single expression, where any tags and whitespace between tags should be removed, leaving only the raw expression.
Topic on Extension talk:TextExtracts/Flow
Or rather, the alttext attribute could be used for any HTML tags that provide it.
As of now the TextExtracts extension has no knowledge about the Math extension. This is a reoccurring problem with many extensions, I'm afraid.
May I ask what the use case even is? Where does this text appear? I know the team around @Physikerwelt worked on Popups support for Math. But that skips TextExtracts entirely, as far as I know.