The text should be -
"Look you're about to reach the end of the game. That means the game will end. That the game will end means that you won't be able to go and do anything else. That's why it's the end. We're telling you the game will end if you continue. In a very conclusive way. Finished, over, done, no carrying on, no going back to to find the NCR still totally intact after you've enabled total victory for the Legion or anything that renders this imminent and final ending totally meaningless like that. It's a story, and that story has an ending. What we're saying is if you plan to do anything else, don't carry on with this bit, click "I'm not ready" and go and do it now, otherwise you won't be able to. Then come back when you are ready. Have you got that? The game is about to end. It's about to finish. We cannot stress this enough."
*Reads Msg* But wait... It still does not explain why I can't play past the ending!
I do hope that anyone who does make a thread asking this either:
1. Misunderstood the message in the box and only needed clarification as to why they cannot go past the end.
2. Forgot to put a few more SPECIAL points in Intelligence.
3. Was pressing the "skip to the next part already!" a bit too early and too much.
4. Can't read.
5. Or simply wants something like Broken Steel to happen, even though it will never come.