If you're a developer working for a company and you have your choice between an MIT|BSD library and a GPL library that, on a technical level, work equally well, it's a hard sell to choose the GPL library.
Consider...
"Well boss, if we use libfoo, we'll have to disclose our source code since it's GPL. There are ways around it by doing things like writing LGPL wrappers and dynamically linking it, but we'll have to distribute THAT source code, instead. Plus, you may want to run this by legal, since the developer has outright refused to sell non-GPL licenses..."
Versus...
"Well boss, if we use libbar, we can just use it since it's MIT. If we make changes to it, we should contribute them back, but we're not obligated to do anything except keep their copyright notice."
With that in mind, is it any wonder projects like llvm and musl are popping up and gaining the support of large companies that use them?