Why do you ask?
grok came up with this:
Some libraries implement free data formats that are competing against restricted data formats, such as Ogg Vorbis (which competes against MP3 audio) and WebM (which competes against MPEG-4 video). The success of the free format requires allowing many proprietary application programs to link in the code to handle the format. For instance, we wanted nonfree media players, especially appliances, to include the code for Ogg Vorbis as well as MP3.
In these special situations, if you are aiming to convince proprietary application developers to use the library for the free format, you would need to make that easy by licensing the library under a weak license, such as the Apache License 2.0.