My guess is something happened to the site that caused their hosting provider to take them offline. More than likely spreading malware or spam emails, as their registration is still valid:
Of the above, the only thing that jumps out to me is the blacklist by backscatterer, but thats more than likely the SMTP server that is hosting hundreds if not thousands of other domain email accounts so it may not even be lionfishlair thats at fault. (theres alot with that site that doesnt adhere to best practices, and a good sysdmin could address all of these in a few hours but thats another thread entirely.)
Its very common for a malicious actor to break into less secure web properties and either host malware or use their SMTP services to send spam. My organization sends and receives ~120,000 emails a month and I'd wager we probably get ~12,000 spam emails from compromised domains in the same time period.