It seems SVB didn't account for the fact that there was a strong correlation between the source of their money (tech propped up by low rates) and their investment risk (bonds/loans propped up by low rates).

I'm honestly unsure if we can ascribe this to to incompetence or greed.

You're borrowing at a lower yield to lend at the higher yield, and the risk is that you have to liquidate before the long one is mature.

Traders do this all the time, because every day you carry this position you're making the difference in yields.

The risk is always the same: the value of the things that give you the yield may change by enough to wipe out the interest difference.

It was a risky move but one that could have panned out if the deposits had remained.