Different industry, different priorities. Almost none of the Y2K problem was in control systems, embedded systems, or the like (a mailling list I'm on was considering creating "Certified Y2K compliant" stickers to put on our pre-electronic engine management cars. We were also considering "Warning: this automobile has not been tested for Y2K compliance" stickers to put on cars on used-car lots, but I digress). It was almost all in the financial, insurance, and government-regulatory etc areas.
But even given that, I'm not quite sure why you think waiting until your bank was suddenly in regulatory non-compliance on 1/1/2000 and starting to fix it then would have been better than spending a couple of years getting it fixed so the customers (and more importantly, the regulators) didn't notice -- the fixes had to happen in any event, the only issue was when and how panicked.
As for your ATM example: if you'd been the manager in charge of the software for those machines for your bank and they'd quit working on
1/1/2000, you'd have been looking for work by some time early that morning. And firing you would have been the vice-president you report to's last official act (with probably several layers of severed heads in between) as well. The only things more important than keeping uptime for customers are backup and regulatory compliance (and in banking, regulatory compliance includes backups).Nor on my machines. But (1) my machines don't have anything major on them by the standards I'm describing, and (2) everything had been fixed in advance -- which is the point.