In their defense, they didn't help the FBI, the Swiss government did. Proton mail had to comply with the local laws. I don't think the Swiss government HAD to send it to US, but they did.
The real issue is these guys made the mistake of thinking any of these emails are truly anonymous and actually linking it to personal identity. They aren't and you should take EVERY precaution if you are going to engage in illegal activity. It's like they used a VPN to hide their Internet activity..... To then go buy something online, with their own credit card, with their name and address tied to it..... And then expected the vendor or bank not to submit to a subpoena.