I used to work at a credit union in IT. I can confirm financial institution laziness knows no bounds. Separate from their laziness is the vendor compatibility. I can't count how many vendors do not update their software to run on modern browsers and relied on specific IE instances. Adding to all that is just the institution itself having decades old hardware and software because modernizing things can be incredibly expensive. The core my company used was incredibly outdated Unix and required a ton of different middleware just to make sure we were compliant where absolutely necessary. If it wasn't necessary nothing got done. And that's better than a lot of banks that could be running on some COBOL based core. Completely redoing the core will affect every middleware crap solution they've patchworked together to keep running over the past few decades and will be insanely resource, cost, and time intensive.

Even these days at my current company I run into this shit. Huntington bank requiring IE for check processing, or SAGE DB software requiring 2013 Access or else it won't work. These are huge companies still utilizing outdated piles of garbage.