Everyone will die someday, a large percentage will die in a very painful manner.. If you had a way to make sure everyone dies at the same time but in the most peacefully painless way, wouldn't you be saving billions from future pain?

Also dying at the same time, they'd never have to witness their loved ones die which brings emotional pain.

Now, hopefully most would see this as idiocy and immoral, but there's someone out there who's a closet Thanos, thinking this is a brilliant idea.