To excel at math requires focus. When I see Computer Modern I see an author who didn't get distracted choosing a better font. Not just undergraduates.
We need to accept that Knuth was an amateur type designer who was genuinely preoccupied with fonts (“I can’t go to a restaurant and order food because I keep looking at the fonts on the menu.” — Donald Knuth https://twitter.com/TeXtip/status/1389329788628783104). He could have delegated the design of the first font for his TeX system to a professional type designer. He didn't.
Knuth started work on TeX's fonts about the same time that he began work on TeX and Metafont (1977-78). CM was largely completed by about 1984-86. He was a computer science professor. I'm not aware of any funding he procured to develop TeX. You're saying he had the financial resources to hire a professional type designer for fonts for an academic publishing system of unknown future?