That doesn't matter if features you're able to used are gated on the standard you use. If the standard you choose is based on what your target platforms 'support': no inline for you.
I could understand the concern if it was about portability to other target platforms, or keeping the option of doing so. But in that case, the public standard your current target supports is irrelevant.
So they add a feature not supported by MSVC and don't learn that it doesn't work until someone else tries to build on Windows.
If you choose to use features based on whether they work or not, you don't need to choose a standard at all. But that loses you all of the guarantees a standard provides.