Because in some parts of the world banking is a historical pile of hacks on hacks on hacks held together with bailing wire and twine.

Also banking is a hugely complex problem involving two of the hardest things to deal with, money and people.

It's particularly the case where you have a lot of small banks geographically spread out running a variety of legacy systems all of which talk to each other in weird and whacky ways.

I'm surprised kiting still works though.