XP isn't broken
And if it works fine, and isn't broken, then spending money to replace it is a bad business decision.
Software may be a capital expenditure, and it does depreciate over time. But the replacement lifecycle for an operating system is not 18 months any more. It's more like 8 years because the technology has matured. Unfortunately, Microsoft is addicted to the 18 month replacement cycle paradigm and hasn't evolved.