I have only recently learned this and I too was surprised it's not a GNU project, and even more so it's not GPL-compatible. The license it's essentially a BSD

I have only recently learned this and I too was surprised it's not a GNU project, and even more so it's not GPL-compatible. The license it's essentially a BSD with the (absurd) restriction that you can't distribute the "complete modified source code", whatever that means, but only patches. I wonder what's the motivation.