They want to block Github entirely because Github allows for the free flow of information (politically sensitive information, not just code) and they don't have a way of doing currently without just blocking all of Github... Which would be bad for business, and China also seems to be entering the software business in a bigger way. Actually, if you want to send large amounts of text information to users in China right…
No, I don't think it's about blocking Github. Many of their tech companies are using open source. For China it's safer to have a Chinese Github ecosystem. Just imagine if Github suddenly decide to block Chinese users like they did for Iranian users. It's also strategic for their government and some critical private sector to not put their source code on an American platform. So there are enough incentives especially…
Github is still owned by an american company and it has shown that it needs to comply with whatever foreign policy that washington enacts. It's reasonable want to have a contingency plan that would allow the Chinese domestic software industry to continue to function when things turn sour between the two powers.