Because it violates GitHub’s trademark. I expect them to send the author a cease and desist notice; and if the author is unresponsive or challenges the notice, GitHub will almost certainly initiate the dispute (UDRP) process, which will inevitably cede control of it to them.

For the same reason your diff viewer highlights it: it looks like a scam attempt, not like a clever pun.

You likely will be able to keep it without trouble, but many corporate security systems would flag it.