Most of those do in fact seem to use WordPress for part of their site:

* microsoft.com – uses WP at devblogs.microsoft.com

* digicert.com – may be a false positive, they link to files at /wp-content/ URLs, maybe they used WP in the past and kept the URLs?

* mozilla.org – uses WP at blog.mozilla.org

* nih.gov – uses WP at directorsblog.nih.gov

* forbes.com – can’t tell, my ad blocker breaks their cookie consent screen

* archive.org – uses WP at blog.archive.org

* nginx.org – uses WP at blog.nginx.org

* ebay.com – may be false positive?

We end up with 2/10 potential false positives, and one unknown (and even then, those are huge sites, who knows if they’ve got WP hiding under some deeply-buried subdomain).

I agree with you that Microsoft and TechCrunch probably aren’t FTPing their files in, but even if we assume that only 50% of WordPress sites are doing so, that’s still more websites than the next 10 competitors, combined!

If you think about it, this makes sense: do you reckon your local small businesses have a TechCrunch-level web presence, or are they using GoDaddy? Now consider that there exist many more local businesses than TechCrunches.