One angle to look at this from is that if Slack or GitHub goes down, there's a good chance your competitors are being held up too. It's like an armistice on (your corner of) capitalism. Whereas if it's just your system, you've been put at a slight disadvantage.
Also, unless it's happening every week there's probably an element of, "well it doesn't make me regret the overall choice to use this service, so there's no sense being upset about it".
Also, unless it's happening every week there's probably an element of, "well it doesn't make me regret the overall choice to use this service, so there's no sense being upset about it".