$5k/month was 25% of his pods, so the total was ≈$20k/month. It's entirely possible that self hosting would cost much more than that, particularly as they wouldn't be able to save costs by scaling down.
Disclaimer: Checkly founder.
Of course, given stable demand and known requirements, bare metal can be a great option. But it’s not strictly better than public cloud hosting.
I think it’s just been long enough that people have forgotten the limitations of bare metal engineering.
Not just engineering, but deploying it too. I'm building a whole business around deploying it based at least partially on the fact that it has been forgotten. I've just been doing it long enough that I remember how to do it and it isn't getting any easier as the need for compute grows into even more complex and powerful hardware.