I don't know how, but there must have been some kind of fuckery with the free market for such a concentration within one bank to build.
Discussion
Honestly, it sounds like there was a lot herd mentality at work. The “nobody gets fired for choosing IBM” effect. I have no clue how much of role that played, but I bet it explains some of it.
They were also apparently giving loans to founders that the founders probably wouldn’t have gotten anywhere else so that probably helped convince the founders to use them too.
The galaxy brain capital allocators were once again worse at risk management than the average farmer.