Comment It's about tactics: GPL helps free software (Score 5, Informative) 1098
Background reading:
BSD, LGPL, and GPL are all free software licences. The user gets the same four freedoms in each case (use, study, modify, redistribute). But, using the BSD licence (or the LGPL) takes away an incentive to contribute to the free software project.
GCC's technical advances create a big incentive for developers who are interested in compilers, and for companies with a commercial interest in a good compiler existing for their platform, to contribut to GCC - helping free software whether that's their priority or not. With a BSD-licence project, developers can choose to ignore GCC and fork LLVM instead, so neither GCC nor LLVM benefits.
LLVM weakens GCC's ability to attract free software contributors. That's why Apple funds LLVM.
It's not difficult to see which approach works best: Which OS has more contributors, *BSD or GNU/Linux?