Basically, they don't want to. I don't see any relevant argument made on this text.
>So, one big reason for not moving Krita's development to github is that I simply do not trust them.
>We cannot be forced by a venture capitalist to monetize our projects by adding malware installers. We own our stuff, which means we can trust our stuff.
Whether you agree or disagree, they did in fact make an argument.