I'm guessing that you use cheats and don't realise what sandbox would do to players who don't cheat. We would run out of energy long before we run out of choices. On top of that, it ruins any choice and consequence this game has.Yes, a sandbox version of this game would be perfect for me, again, dont want to bring more work to the dev, just a gameplay POV.
Even with the checkpoints you won't see everything the game has to offer, but have you tried using them? There's a set checkpoint and load checkpoint links in the sidebar when you have cheats enabled.