I don't think it has any benefit for them to explain why. Explaining why just invites argument.
"Oh, you can't pay because we are in Russia, just pay to our Massachusetts subsidiary!"
"Oh, you can't pay because we are in Russia, just pay to our Massachusetts subsidiary!"
It clearly has. There are lots of hackers and security researchers who will make very different decisions depending on if they expect Apple will honor their bounties. Traditionally, people who report security bugs have been treated poorly, and arbitrary rejections certainly helps move the incentives towards the exploit market instead.
... and who knows where that could lead. Why, the rabble might get the idea that they're allowed to disapprove of decisions Apple makes!
I would still call this a "refuse to" vs "can do", but hey, Apple can keep that money - keeps the layoffs away.
It's not the first time we've seen Apple not playing nice with their bug bounty programme, so it's something of a pattern of behaviour. "A show of good will" is exactly what they need.