Because they're leaving the country tomorrow and don't plan on ever coming back. And you offered them a round of drinks or two for them and their other friends.
(Thinking about it, you're probably right - I still feel that's "safe" in Australia, I doubt I'd be prepared to do that in 2025 USA. But then I'm not intending to visit the USA in the near/medium term future, or possibly ever again.)
Because they're leaving the country tomorrow and don't plan on ever coming back. And you offered them a round of drinks or two for them and their other friends.
(Thinking about it, you're probably right - I still feel that's "safe" in Australia, I doubt I'd be prepared to do that in 2025 USA. But then I'm not intending to visit the USA in the near/medium term future, or possibly ever again.)