Last I heard, about 30% of Internet traffic came from XP machines. It was reported that Microsoft hoped to get that down to 15% by the drop-dead date. That, of course, doesn't consider embedded systems.
One needs to consider Microsoft's imperatives as a business. They can't go on forever supporting operating systems or Office software which brings them no continuing income. Subscription software ("Office365") is an answer to their need for a continual flow of income.
There is perhaps a reason why MS has moved to the DOCX and XLSX formats. They are nearer the ISO standard which is used by OpenOffice / LibreOffice as their default. OO and LO read DOCX and XLSX documents without complaint. They can write DOC & XLS. I understand that recent versions of MS Office read OO and LO formats.