Also, their incredible insistence in people upgrading to 10 makes it clear they learnt with Windows XP that people don't rush to upgrade to a new OS if they're happy with what they have. Also that they had a plan to make a lot of money off Win 10 even if people upgraded for free (increased used of MS' services (bing, hotmail, their cloud service), data gathering, people buying from the Windows Store
And pretty obvious that "Windows 7 increases maintenance and operating costs for businesses" actually means "we'll make less money if you don't upgrade".
Maybe if you gave people what they want people would willingly update to your latest OS instead of rejecting it even when given away for free.
Make a Windows 7 with the internals of 10 and I'll upgrade.