We say a lot about Simon's drive to live, but I keep thinking about Simon's obsession with death and being killed, and it can mean so much.
1. More than once, Simon snaps at Ava to the tune of "if you want me dead/kill me so bad, why dont you do it yourself?!";
2. When she bids him get a sample, he quietly (though a bit testing the waters) asks if the COI won't just kill him once he's done with the mission;
3. When Elli threatens him to not reveal the light to others, he dares her by shouting "you want to eat me?! then come and try!" even though she's been trying to be helpful if confused and unfocused through it;
Everytime, there is an explicit assumption by Simon that everyone wants him dead. Now, that can be easily explained by Simon being blamed for Filament Station, thus i doubt the COI has treated him all that well.
(That's already proven by the handcuff burns on his wrists and his general grimy state. You don't get this dirty with just a couple days in a sub.)
But consider also that it may go deeper than that.
Often cults cultivate a mentality of us against them, a paranoia that the entire outside world is against the in-group. They want to destroy us, separate us, demoralize and break us. They want us gone. They want us dead.
Considering Eden as a death cult, one's death is food for the Tree, one is never truly lost or gone, because they are reborn in the Tree. To die is to become. It's not a big stretch to suggest that for Eden, the best thing you can do in life is prime your body for feeding the tree, and making sure it finds its way to it. A lost body is a body denied of becoming the soil, or returning to the Tree, of fulfilling its purpose.
The COI has probably made this a recent policy given the whole loss station. Putting your enemies to work for you on the most dangerous positions to spare "your own people", and maybe rewarding the ones that do survive since they've "earned their place in the Consolidation", is also nasty. Regardless, the point is that they say they want you to live and join after you've made amends, but they couldn't care less if you die far from home.
Putting those two together, the message becomes: they want to take us away from the Tree. They want us to die far, and never to become soil where we belong. Separate from home, from our loved ones, from our fellow fallen. They want to starve the Tree of what it has left. They want to kill us, but most of all, they want our salvation to suffer too. They want the Tree to starve.
He has plenty of reasons to believe everyone out there wants him dead, and the cult conditioning cerrainly doesn't help with that.
Now, we know that while Simon does not fully buy into the narrative of Eden, he does care a whole lot about the Tree. If its religious or some other reasoning, the Tree and the Pendant move him emotionally every single time.
I won't diminish his will to live or his drive for survive. Regardless of motives, his life is worth keeping regardless and that's not up for debate. But I do find it interesting if his reluctance to die comes at least in part because he refuses to die there, where any chance of ever returning to the Tree is nill. He may not fully buy into the religiosity of Eden, that the Tree is God or related to it, but he can be atheistic on that front while still holding significance to becoming the soil again.
With that lense, him turning into the Blood Tree in the end matters even more. He's not only refusing to become part of the blood, refusing to be beaten by the Eel or be one more lost soul and body in the vast void. He literally willl himself into becoming the soil AND the Tree, a new one, away from Eden's control.
