Among the reasons are:
* https://en.wikipedia.org/wiki/Mandy_Rice-Davies#MRDA
* AFAIK, de Icaza was no longer involved by then
Additionally, FWIW, it's not "lots of times".
But the MS threats are a matter of widespread legal record. This is not some kooky opinion of mine. This happened, it's documented, and the responses are too.
For instance, Novell (owners of SUSE then) and Red Hat were specifically named:
https://www.linux-magazine.com/Online/News/Patent-Suit-Filed...
RH responded, denying the claims:
https://www.linux-magazine.com/Online/News/Red-Hat-Calls-Mic...
https://www.linux-magazine.com/Online/News/Red-Hat-Seeks-Def...
So did Canonical:
https://www.itnews.com.au/news/ubuntu-repels-microsoft-paten...
https://www.cyberciti.biz/tips/redhat-ubuntu-linux-rejected-...
Novell meanwhile signed a patent sharing deal:
https://www.cnet.com/tech/services-and-software/microsoft-ma...
Later extended:
https://www.zdnet.com/article/microsoft-and-suse-extend-micr...
This was my current employers on it, but long before I ever wrote for them even as a freelancer:
https://www.theregister.com/2006/11/20/microsoft_claims_linu...
Everyone covered it. It was THE big new story about MS versus Linux.
https://money.cnn.com/magazines/fortune/fortune_archive/2007...
https://www.engadget.com/2007-05-14-microsoft-linux-and-othe...
https://arstechnica.com/tech-policy/2007/05/microsoft-235-pa...
https://www.networkworld.com/article/2355239/microsoft-claim...
It was already a thing back in 2004:
http://news.bbc.co.uk/1/hi/business/4021775.stm