Ideally, before the cold death of the universe, I want to transition my body into a higher dimensional body. So I'm entirely in support of your argument.
However, digitizing our brains, or any other transition away from the status quo right now is not only not currently possible, it is currently unimaginable. There have been no prototypes, no significant research, not even any real theories on how to accomplish such a task. Even repairing/repurposing parts of our current bodies is a giant challenge. Hell, we can't even appropriately map our biology or understand how they actually work.
Transitioning away from biology will take time. However, until that day, we need to stay alive and we need more resources. Becoming multi-planetary is just one "safe"(predictable) step towards the future you would prefer.