The real costs are the ~$100m they spend a year on developing GitHub and providing it for free to most people - including free CI.
They charge 3x the cost price for runners so that they can actually make money. This change is so that they can't get undercut by alternative hosted runner providers.
I do think they could have just explained that and it probably would have been more palettable than their "we're making it cheaper!" lie, but I guess there are also a lot of people that still think the only moral pricing is cost plus.