I wonder why he doesn't have a secretary. Isn't he like one of the top mathematicians in the world? Why the heck are they having him do drudge work?

Profs don't get secretaries. There's usually one admin assistant for the entire dept. and they're busy with applications for admissions, scholarships, grants, etc.

Or grad students, for that matter. The notion that Tao should have to monkey around with Excel in person is just bonkers.

He'd be a seriously bad professor if he wasted the time of the people he was supposed to be teaching with copying badly formatted data for a talk.

mathematicians do not do math all day. there is probably a point of diminishing returns where more doing more math is not useful.