The average bank/company would rather have an average solution maintained by 10 easily replaceable average developers than a nutty, smart solution only understood by 1 highly talented developer.
You could also say that the average bank/company should have learned from previous mistakes doing exactly that for many decades. Select a language that is well tested, understood and supported. Set a limit on cleverness and instead focus on maintainability and simplicity.
If only. In my experience, banks end up building a solution that is maintained by 100 mediocre developers that a reasonably smart developer can't make sense of when it behaves erratically or has extremely poor performance.
I described the theory. You have described the practice :)
Which was precisely my point (and I agree with all the responses in this thread), though my wording and light sarcasm seems to have been a bit too dry, and didn't quite take up as intended.
Keeping skill barriers low keeps wages low as well.