A matter of fact is that nothing is stopping Israel from annexing large parts of the western bank, especially when it has the US backing. What is stopping the Israeli Army to move into those parts right now?
Their biggest concern is their survival in the Middle East which won't be possible as long as there exists enmity between them and the 6 Arab states they're surrounded by. In the long term, it will materialize into long problems and fights.
So they're addressing that concern, if that concern can be traded for pre-67 borders, then you can't get anything better than that. If the agreement is broken, the enmity returns.