Many of these stocks are still trading far cheaper than they did just a few years ago. He noted that First Horizon used to trade for $39 a share but now sells for under $11, while Huntington used to trade at $29 and now is under $7. That's very cheap by historical standards, and why today's selloff had little effect. But more important than their cheap valuations is how banks make money. Cramer said banks will pay you 0.81% on a five-year CD but will, in turn, invest that money in a five-year Treasury yielding 1.38%. That might not seem like a big spread, he said, but it's more than banks have seen in a very long time and Treasuries will certainly see rates rise faster than the banks will raise their CD rates going forward. Institutional investors in bank stocks only care about one thing: net interest margin. Now that rates are on the rise, these investors will be returning to the regionals, which is why individual investors should be as well, Cramer said.