> Was there something particularly incredible about SVB that led so many businesses to use it, and use it solely?
My general understanding is that with many banks, if you walked in and said "Ya a bunch of people gave us $10M, and we're basically going to be cash flow negative for the next decade, will run out of money unless people invest again, and we're 90% likely to be out of business in 5 years", they'd likely not want to work with you. They especially wouldn't be offering you additional lines of credit.
SVB on the other hand seemed to be understanding that the business model of SV start-ups was different than more traditional companies, and was a lot more willing to work with them and accept a level of risk.
It sure seems now that the risk associated there didn't necessarily work out (perhaps the biggest understatement I've made in a long time), but that's the reason that so many businesses in the tech start-up/bay-area used them.
As to why they used it solely, I can't answer,m but I've heard that raising debt from SVB required you to keep the majority of your account holdings with SVB (which really doesn't seem that unreasonable)