That code was published in a publicly available paper. The algorithm was known. Blender just implemented it first. There were plug-ins for a lot of the other programs to implement it there. Nothing nefarious about that. They were just slower to the punch in that case.
As for your question about the GPL, that’s not allowed either. Even if your code links to a block of code that’s licensed under the GPL, you must have your code in a GPL-compatible license. This is why some people have problems with the GPL (as shown in this thread and ones like it). It’s a two-way street. GPL code can’t be easily integrated with closed tools and closed tools can’t be easily integrated with GPL ones. There are perfectly legal work-arounds of course, but that’s something better kept in that other thread. 