I mentioned this in another thread. Services like Stripe-Atlas that helped founders setup businesses offered SVB as the banking partner since 2017, I think (now they have other options--Mercury and Novo). For a founder trying to bootstrap, a single-window that took care of all the nitty gritty of starting a business is a big time-saver. So, many founders might have opted for the convenience.

The banking services and treasury operations should have been the responsibility of the CFO of these startups (if that role existed). All startup CFOs would now be reviewing their treasury management function seriously post-SVB-blowout.

source: I considered Stripe-Atlas a few years ago and decided not to go with it for my company.

Aside from the frequently mentioned aspects that many times SVB is the only reasonable place to even get an account if you are a startup (something that is changing now thanks to things like Mercury and Brex), many services will push you to use SVB, outside of VCs. For example, accounting and management services like SVB for the simple reason that SVB has basic features like "user groups with different privileges, so that some people can issue wires but not approve them, etc." BofA small business is really hard to work with. Some of it sadly comes down to super basic stuff like that.

https://mobile.twitter.com/jonwu_/status/1634250767971532800 sounds like a plausible reason. SVB was offering great deals in return for being the exclusive bank and you parking all your cash with them.