LLVM exists because its original developers wanted to do research, not because of GPL and at the time there wasn't even a C compiler for it, not to mention that GCC wasn't designed at all to do what LLVM did.

The license angle with Apple did happen because of GCC's switch to GPLv3 but that came years later - and GCC still wasn't (and AFAIK still isn't) designed to be used like LLVM or (later) Clang, like using it as a backend for IDEs, analyzers, language servers, etc. The two projects aren't interchangeable with only the license being the thing that differentiates them.

I don't even understand how you can point to LLVM as an example of this failing. GCC is still alive and well, and perfectly suited for the task it was always intended to fill. People that wanted a commercial C compiler always had the option to purchase one at-cost, GCC was intended as an alternative to that process, not the alternative. It may be hard to remember, but less than 50 years ago squabbles over compiler licensing was what most developers had to deal with.

Respectively, LLVM fills it's own gap nicely. It has the classical BSD-like issue where hundreds of unique and disperate forks exist with no roadmap to bring them together, but that's also technically a "feature" of each license and not a bug. If GCC developers felt their job was obsoleted by Lattner, there wouldn't be a reason to update and maintain it. The end result has been healthy competition, accountability for either team, and better optimizations for everyone using either compiler.