If they didn't refund him, maybe he'd jump to a different provider, maybe people would see this and not sign up for AWS in the first place, etc. By refunding him, they likely keep a customer, don't scare away other potential customers, etc.
I loathe the day when I'll have a similar problem but, as I am not a Twitter user, I won't have the luxury of getting my problems fixed.
In my anecdotal experience, just submitting a support ticket explaining what got screwed up and you made a mistake and how you’re going to rectify it so it doesn’t happen again is usually enough to get the charges refunded. And even if you don’t submit all that, often they’ll just prompt you for it.
For example, when a legacy account got compromised and rang up like $20k in charges running a bunch of servers to mine some sort of crypto, we asked for a (totally undeserved) refund and they just had us rotate all our access keys and refunded it.
The support is part of the reason why I prefer dealing with AWS. I know from my time managing over a million bucks a year in AdWords spend that the reason Google’s support is non-existent isn’t because you’re not a paying customer...
So they just waived it as it's better press.
Through I'm surprised they waved all of it, I would have expected half or so to be waved but then it doesn't really matter for them.
It seems to be pretty common not just for Amazon to be nice in case of such mesup's so that it is less likely to scare away people.
TL;DR Individual feels wronged, pushes things off AWS at their employer, AWS loses much more than $3k refund.