Aren’t lobsters supposedly “immortal” as well? They don’t revert in quite the same way, but they are capable of dealing with telomere issues due to something within their biology. They continue to grow in size, so they find it more and more difficult to hide and avoid being eaten; so it isn’t quite like the mentioned jellyfish. But
I just remember this because one of my top rated comments was about using the science behind the telomere “fix” in lobsters to extend human life, and having to compete with my great-great-great-grandchildren for potential mates due to nobody ever dying.
Edit: Scrolled down and more or less got my answer. They die because of predation, but also because they lack the ability (eventually) to sustain the energy levels required to keep up with their size. So, they eventually do get too big and will eventually die no matter what. However, I would be interested to find out if there have ever been mutations in lobsters that create “dwarf” lobsters that are unable to increase in size beyond a certain point, thus never having to deal with the size issue, and because their genetics are not an issue, they would be theoretically capable of existing for a very, very long time.