There you go. While I have to admit that the blog entries do not prominently talk about the reasons why the relicensing was done, it's not like there is no statement at all in that direction.
Note that the FOSS alternatives to the VLC backend/plumbing code are all LGPL or even more liberally licensed. This reminds me more of the decision to make glibc LGPL rather than GPL - plenty of alternative libc implementations exist. Thus for third-party devs there is no incentive to use the more restrictively licensed library.