Yes, the final analysis showred that Windows 7 systems were the most affected by WannaCry. And they were targeted for more than a year by Microsoft with the multiple "upgrade now to 10" ads delivered through the security update channel. And I personally had the computers which didn't work under Windows 10, and worked correctly under Windows 7, so I really understand those who disabled auto-updates.

Not to mention that also afterwards there were Windows 7 patches that kept one CPU core 100% busy for days!