I understand it, even if I think it is a bit silly and probably evidence of a mental sickness. The survival instinct is an important one for getting life to where it is.
Problem I have with immortalists isn't that they have some desire to live forever, it's that they rarely are able to articulate what lives forever. Self is a construct, an narrative abstraction created by our minds that has utility as regards our functioning in the world, but is ultimately not real. I am not the same person I was 5 years ago, nor will the version of me that exists 5 years from now be the same as me. There are probably several people out there who are more like 5-years-ago me than I am currently, but for some reason they aren't considered to be the same person.
What is it that makes me me? It can't be memory, because memories are extremely fallible, and often confabulated. If we are our memories then we have forgotten most of who we are and will continue to forget ourselves as time passes. If you erased my memories somehow, you'd still likely consider me the same person anyway, so clearly memories aren't me.
Of course, even forgotten experiences leave some kind of mark on our being, but just by existing we leave our mark on the people and world around us but we don't consider those things us, do we?
And clearly anyone who imagines a digital-self in their future doesn't consider their physical form to be them either, so what's left? Illusions and abstractions, a heuristic notion of self that has utility but not reality.
Sure, go ahead and solve "immortality", I don't have a philosophical objection to the concept. What I have a problem with is the insistence that death is some kind of fundamental evil we must place a high priority on solving. Some would go so far as to preserve their own lives at the cost of many others, so terrified they are of something that has basically already happened to previous versions of themselves. Its perverse.