If you think self-hosting doesn't randomly go down, you have never done self-hosting.
In the last few months we had a server that physically crashed and had to be replaced, we had a bad kernel that paniced randomly and a gitlab upgrade that failed in the middle.
Is you team equiped and ready to handle these? If not, don't self-host anything critical to your company, or your costs, downtimes and losses will be much much higher.
this always comes up, and it's one of those things that's obviously true on the surface until you understand context.
I have a self-hosted gitlab instance and it has much higher uptime than github in the last year. At some point a weekly downtime is going to trump any potential random outages.
The major difference might be your ability to affect those outages (positive or negative) because humans are the primary cause of outages, and you can restore service to a gimped passable state if its your own thing.
Even for bigger companies that need more uptime they can at least give a shout out to everyone that it will be unavailable from X to Y, it doesn't just go down randomly with no notice whenever github decides to push a release.