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...