It's not as simple as moving everything onto a more modern infrastructure. At this point, the financial system is so intertwined with its COBOL roots that it would be like trying to simultaneously replace all of your veins with fiber optics. A switchover is theoretically possible, but if something goes wrong, the financial data for millions of people could vanish.
Since it would be impractical to make everyone temporarily withdraw all of their money until the problem is fixed, geriatric programmers are making good money running firms that specialize in COBOL. Meanwhile, the industry is rushing to train young programmers (and rehire the old guys they fired because they thought their skills were obsolete). Further compounding the problem is that programmers of the original COBOL systems rarely wrote handbooks, and deciphering someone else's computer code 40 years later is like trying to communicate an elaborate sexual fantasy via slide whistles.
And it's not only banking. NASA once desperately needed to find programmers who knew Fortran to communicate with their Voyager probes. These are by no means insurmountable problems, so don't panic and put all of your money in Dogecoins tomorrow. But it's kind of like suddenly discovering that we have to teach thousands of people Latin to prevent the English language book industry from collapsing.