" . . . isn’t Vernon Hill, one of the bank’s founders, tempted to build an IT system of his own? I hate programmers, replies this dyed-in-the-wool entrepreneur. They only cause trouble." Spoken like someone who's been there on a few projects.
The answer tends to be that they don't, they get lucky or they get unlucky. They don't have any protections from getting taken to the cleaners. From spending $10 million on a VBA + Access abomination that's far more trouble than it's worth. But they may be so unsophisticated when it comes to software that they don't know they've been taken for a ride until years later.
Compare that to, say, construction of a new bank building. A bank president knows that if they spend $X million they'll get a new building, with high probability. There may be some problems along the way but they for sure won't end up spending $X million on nothing, or on a cardboard box with a "BANK" sign written in crayon on the side. It's understandable that they might be a bit leery of dipping their feet in the IT waters.