CNBC's Jim Cramer has spent hours trying to figure out why the bank stocks failed to rally after the Federal Reserve's announcement that it would hike interest rates four times in 2018 instead of three.

He reviewed all the conventional wisdom: that a flatter yield curve is suppressing what would otherwise be stronger lending revenues; that mortgage loans are tapering off because of higher rates; that Wall Street is still awaiting the Fed's stress tests to make a lasting determination on stocks like Citigroup, J.P. Morgan and Goldman Sachs.

But the "Mad Money" host still wasn't totally satisfied.

"As I wrack my brain, I come up with one plausible — and yes, existential — answer," he said Friday.

"There are plenty of younger portfolio managers who think the banks are like Sears and J.C. Penney: they're old-line brick-and-mortar stores that are about to lose their relevance thanks to all sorts of new technologies from bitcoin, blockchain, PayPal [and] Square," he continued.

Cramer has seem some money managers "hide" in financial technology stocks like Mastercard, Visa and American Express to get financial exposure without owning shares in the banks.

"The others, though? Well, they're about obviating the banks altogether and that may be a real part of the problem," he said.

His favorite pick was PayPal, parent of millennial-happy payment services like Venmo that spun off from eBay in 2015.

Calling PayPal "the Amazon of banking," Cramer said the payment processor has grown into more of an "online banking company that cooperates with everyone and has gone global."

"It's the international bank to the unbanked, a huge group as roughly two billion people lack banking access right now," he said. "At one point years ago, Citi seemed to be really taking on the mantle of the tech company, but it's pulled back. It's no longer that kind of thing. Bank of America has the best online division, but it pales in comparison to PayPal."

Square, a payment technology play helping smaller businesses accept credit cards and other payments, has also made strides in presenting an alternative fintech investment, but shares have gotten costly at these levels, Cramer said.

"Then there are the potentially existential threats that I just mentioned: blockchain, which some people believe could possibly end the banks' hegemony over stock clearing, and cryptocurrencies, which are the populist insurgents of the blockchain movement," the "Mad Money" host said.

Blockchain, the notably secure software powering cryptocurrencies, has become a focal point for big bank leaders amid the rise of crypto popularity. Many are said to be developing their own blockchain applications.

The popular, yet volatile digital currency bitcoin was down slightly at the end of Friday's trading session, hovering just above $6,500. Competing cryptocurrency ether soared 9 percent on Thursday after a Securities and Exchange Commission official said it was not a security.

"I'm not saying this is the right way to look at banks, but it's certainly how younger portfolio managers view the group, and they are winning right now judging from where the group is trading," Cramer concluded. "As I see it, they are the true reasons for the group's underperformance and until the banks regain some visible earnings momentum, their stocks will not be able to get their groove back despite the additional hype that might be coming our way."