If only 2 years ago somebody said GitHub would be no longer relevant soon, nobody would believe them. GitHub was the undisputed leader in repository hosting [..]

GitHub has done too many great things over the years, so I hope it remains, but there is obviously an earthquake going on.

Is the 'earthquake' referring to the frequent outages over the last couple of years, and if so are those outages because Microsoft can't keep up with the demand?

It's closer to 'too relevant' than it is to 'no longer relevant'.