Several people in the comments seem to be blaming Github for taking this step for no apparent reason.
Those of us who self-host git repos know that this is not true. Over at ardour.org, we've passed the 1M-unique-IP's banned due to AI trawlers sucking our repository 1 commit at a time. It was killing our server before we put fail2ban to work.
I'm not arguing that the specific steps Github have taken are the right ones. They might be, they might not, but they do help to address the problem. Our choice for now has been based on noticing that the trawlers are always fetching commits, so we tweaked things such that the overall http-facing git repo works, but you cannot access commit-based URLs. If you want that, you need to use our github mirror :)