Our brains aren't big enough to hold an eternity of memories, so you would forget who you were to make room for what you'll become. What's the point of immortality without continuity? That's a living death.

And forget about actually cheating death. Imagine if somehow you survived long enough to witness the heat death of the universe. Stuck on some Dyson sphere around a white dwarf for billions of years as the entire universe fades to black and all the things you used to do become impossible because there isn't enough energy to do them. And in the end you still get sucked into a black hole like everyone else, wondering if you are the last living thing in the universe.

Nah I'll just die when the sun still shines.