Disclaimer: I have not been to B school but I did do all the prep & tests. Perspective: I’m an engineering grad from a presitigous university.
These are secondary reasons:
the intelligence of the students. So, when people do go to B school, it's common (and turned into memes) that they look for undergrad developers to build their products. Secondly, at CU you will find the smartest students in the world. People that live in your very dorm will not only have the passion for solving problems, but the intelligence to execute on startup ideas. (my friend who lived on my floor in Freshman year just raised $3.5mill for his startup)
Direct connection to other schools. CU is the place to connect. In addtion to my prev. note about the small physical footprint, there are an overwhelming number of events to connect clubs and students across school! I met loads of PhD, MBAs, etc etc in my time. Also crucial to mention that these school are the top in the world. CBS, Columbia Engineering, Politics, Economics, Columbia Law!!!, Columbia Journalism.
There also exist multiple platforms to provide direct connection for thse interested in start up (look up Build Lab - I only heard about this in my final year!!! connects CU students to new CU startups. and helps connect those with ideas to those that have talent.
the location. The best place in the world to build a company. You have the offices of the biggest Venture Captical firms a short commute away. (VC firms provide money to startups). You have the HQs of every industry down the road. You have all the News attention.. opposite a Freshman dorm (Columbia Journalism School is #1) but also.. down the road. All the best and brightest students/people from around the world end up in NYC.
Youthfullness. Undergrad students tend to be at a point in their life that they can weather the structural downsides of builing a young company. Financial safety net, no kids and no responsibilties, etc.