[drran]

Yes, it's because of GPL restrictions: if you use my code, then I can use your (to some extent), so proprietary developers are forced to cooperate, which everyone job easier.

Linux is used by whole planet, but it's not a burden for Linus Torvalds.

Same for KHTML -> WebKit/WebCore -> Blink (LGPL), which is used even by such GPL haters as Apple and M$.

[trasz]

Same for Postgres and multitude of other liberally-licensed software.