People are already saying things like "We need a plan B in case we urgently need to deploy a fix to production, and GitHub Actions is unavailable again".

But in general, it's not feasible to do everything in house.

And I don't think that GitHub is devoid of SLA: https://github.com/customer-terms/github-online-services-sla

The issue is that they're not achieving two nines uptime in practice.