Hmm, that seems like a pretty cynical point to make. He still deeply is in the field of mathematics, as a math educator. He even makes this exact point in this video, that communicating math is still a hard and respectable part of the profession.

As a math educator doing what you love you require an audience.

Its kind of in Grant's incentives to push the interest for mathematics, because without an audience he won't be able to keep doing what he loves.

Like, my old uni has a history department, and had an Egyptian history teacher. This was at some point deemed a pointless use of resources because there was no role in society except for teacher of the same subject after that, and she was offered a role in admin. She was not happy in that role.

Sorry I didn't mean it to be cynical, it just came to mind