Could you provide details on how you plan to be more reliable with a self-hosted solution? what kind of archtecture would you use? how many people will be involved in maintaining?

I would choose self-hosting for small to medium size teams any day. I can't fathom why people choose not to self-host at this scale. Your data. Your control. Your network. Your infrastructure. Your responsibility. Are people becoming more afraid of responsibility these days?

Self hosting GitHub is an option as well. We've been self hosting GitHub Enterprise for years and it has had no downtime other than during scheduled updates (at night, when nobody's at work).

self-hosting requires quite a bit of scale to be more reliable, otherwise you'll most likely still have possibly longer outages, just at different times.

You can self-host GitHub too. Or BitBucket.