Nobody really cares about the pedgree of a computer programmer. There are some narrow areas where they may want to have a highly credentialed person serving as "chief scientist" or something, to impress investors. A startup may want to tell investors that "our technology team is lead by an MIT PhD in AI" but beyond that the credentials of your dev team are not marketable.
Career fairs are a very effective advertising route (guaranteed real people, high chance people are developing in relevant fields, chance to network with future recruiting wings) on top of a way to try and get interns or junior level candidates. Especially small local businesses who have no chance attracting national talent.
To tell people that you aren't interested in I'm advertising (a business's favorite thing) paints a dire situation, reflecting how bad times really are. Especially in an area like SF
And as a fun little dystopia to end off on, there are many non-school career fairs companies go to in 2023/4 with no intention of even interviewing. A few will straight up tell you they aren't and just want to "bring brand awareness". Yay economy.