[Cojen]

One word: patents. GPLv3 has wording which suggests that you need to give up rights to patents when you contribute. If you're a large company, with a large patent portfolio, this becomes an expensive endeavor. Either you give up patents (which might have value), or you do an exhaustive search to verify that no patents are being infringed.

[jabl]

Apache 2.0 has similar patent language as GPLv3, and is the current bigcorp favourite open source license, so I'm not sure that's correct. Or am I missing something?

[Cojen]

This is true, however I think that the perceived "viral" nature of the GPL gives the impression that patent invalidation can easily spread around to proprietary projects as well.