GitHub was founded in 2007. They were acquired by MS years ago. They should be well beyond any startup culture of "move fast at the expense of reliability".
() They were founded in 2004, that's 10 years in. By that time in 2014 they had 800M+ monthly active users and $12 Billion revenue; and they had this culture internally until this point.
GitHub is an enterprise product crucial to tons of businesses.
Cultural comparisons between the two really shouldn't apply.