I once worked for an organization that had a handful of small customers holding on to older browsers and operating systems. They represented <1% of our customer base and an even smaller % of our transaction volume.

But this was a government-contracted non-profit and it couldn't just write them off as customers. So the organization decided it would be cheaper to help these customers upgrade their legacy operating system, browser and enterprise apps then to continue to try and remain reasonably compliant with their browser.