I was going to make some snide comment about black hats being excited to pwn 1% of computers or whatever W7's current market share is. Then I went and looked it up. netmarketshare.com thinks it's still above 40%, with minimal movement over the last two years. Shows what I know.
FWIW I've done some limited consulting work with senior citizens. Two observations: A) they like their systems the way they are, so changes of any kind (especially to the UI) are upsetting/unpleasant experiences, B) they are on fixed incomes so hardware/software upgrades that cost more than some de minimis amount are put off / ignored. My prediction - this cohort is going to get slammed at that EOL date.
The people who don't replace their Windows 7 probably don't care about security. Furthermore I don't don't know any Linux distributions to guarantee support for more than 10 years without cost. And Apple/Google seem to take an even worse stance.
chromeos in particular is a mixed bag. Great for security (not privacy though) while supported, but only supported for about 5 years. This is for x86 hardware, where traditional distros will support them almost infinitely. Only 32-bit hardware is slowly getting deprecated, but any x86-64 hardware that you can get your hands on is still supported by all linux distros.
But the people hit by the huge botnets of unpatched Win 7 machines care.
If they cared they will pay for support or switch to Win 10 or switch to another OS (but which one gives >10 years of free updates?)
Companies who don't want to get DDOS'd should pay randos on the Internet to update their computers?