The hacker group gives part of their profit to charity and does not attack hospitals or non-profits.
If they also prove they donated to charity via Bitcoin I would assume some legal rights for the victims to claim this money back off the charities. (And it looks like they've given $20k USD to date which is probably a paltry amount for what they've been extracting https://www.bbc.co.uk/news/technology-54591761)
Why would they need positive PR? Exactly how does that help them?
They are attacking large profitable corporations and sharing some money with charities. They're helping solve inequality.
I bet charities take money from disreputable sources all the time.