Why? Who would want all of their financial transactions to be public?
That's what they said about Facebook and Twitter. We're open about almost everything else because the benefits outweigh the costs.
Say you need $50 to buy groceries. What do you do today? You put it on a credit card (at 12%?) or, worse, take out a payday loan. But there are almost certainly friends of yours who would gladly lend you the $50 if they knew you needed it.