At first though, when I read through I considered "this is exactly what Stallman didn't want to happen with GCC! Companies using the open-source parts to power their own proprietary tools".
And then I read at the end that they intend to submit most of the things they've done back to LLVM/Clang.
Microsoft is actually starting to act like one of the good guys.
Morality doesn't need to come into it - they have real incentives to push changes back to master even without restrictive licenses.
It's the "Working with the LLVM Community" section.
Go back an look at history, many companies are evolving towards being more open.
Fast-forward a few years: if people become dependent on the new tool and there's money to be made differentiating their tooling from others, their attitude may change.
The debate about licenses becomes more interesting once a contributor finds themselves in a position of power vs other contributors.
Or maybe they just get tired of having to vet their changes and designs with third parties. Getting code accepted upstream can be a lot of work.