Enterprise licenses, for one - and yes, some of us are running on work PCs. At least one kind of educational institution license group for another - I have one of those that cannot be upgraded.
You’re the one calling it all free to upgrade/free to use. Turns out you are incorrect that anyone and everyone who is capable of running EVE is also capable of upgrading to Windows 10 for free or using EVE Anywhere for free.
Also, CCP has noted the EVE Anywhere beta is ‘no additional cost’ to Omega during the beta test - there is every indication it will be an even more expensive subscription service once it is launched in full.
Look, if someone cannot or will not upgrade right now, and CCP is able and willing to support them as-is, it isn’t hurting you. Your gaming experience is not suffering because CCP is supporting older OSes. CCP is clearly still making a profit off the time going into that population - so the dev hours required to support it aren’t coming from other work, they are being paid for by that population.