I wish NNTP was still alive and widely used - it is easier/faster to subscribe to a newsgroup than to a maillist and once you've subscribed you can see old messages in your client and reply to them (not only new messages like with a maillist).
1. It's easier to set a mailing list up compared to creating a new newsgroup or setting up an on-premise NNTP server (is NNTP as a service even a thing?)
2. Most people have access to email clients (either web based or local applications) compared to NNTP clients.
Personally, I think it would be much better if people use NNTP instead of mailing lists, but doing so would require somoene to maintain the NNTP server and handle account creation for posting access.