Yeah, I admit that it is a possibility. But overall, the whole concept of being revived there still makes as much sense as "you probably don't remember anything about your previous life. However, you can still speak English fluently".

It's Space Magic. Our characters know how to speak, use guns, pilot sparrows, maintain and upgrade their own gear. I just suspend my disbelief and accept this kind of stuff as necessary to keep the story moving. I'm just glad I didn't have to sit through a montage of our characters learning to speak, walk, and poop all over again.

Yeah, I began to realize after around the third mission they didn't think any of this through....

I don't think these sort of details matter much. The idea of the game is to get the players into the action as soon as possible. Our characters will know what they need to know in order to be bad ass action heroes. They're also empty shells (no backgrounds) because we're meant to inhabit them and instill ourselves into this character. Rather than being a puppeteer for an action hero that someone else fully fleshed out, we are the action heroes and this is our legend. It's just like the main character of Marathon, and to a lesser extent Master Chief, were empty shells for the same reason.