Hello, I am the author of VkFFT. When I made VkFFT I wanted license to be like this: your project doesn't have to be open-source, but please share your modifications to VkFFT. I think about switching it to MPL 2.0, is this one better for everybody?
MPL doesn't protect such developers, but it "forces" contribution of changes back to original code. In reality, it's ignored.
Header-only library cannot be compiled as separate library, so requirements of LGPL cannot be met by proprietary code.