They're having so many outages that they've moved from making statements after each event to aggregating them all and write about all of them on a month-by-month basis.
I don't remember when it started getting worse, but if I do a guess, I'd say around 2018 sometime, which I'd also guess is when they started pushing more changes too.
I'm not joking: https://github.blog/tag/github-availability-report/