It's a mindset held over from players of 5th Edition (myself included for a while). 5E had flat out in the movement phase, but models could not disembark from it. Wrecked results than destroyed any models that could not disembark from a wrecked vehicle. Strangely enough, this left a loophole where explodes results kept the passengers alive.
Now that flat out is a shooting phase move, they've removed the "cannot disembark" line, so now wrecked allows them to disembark according to the normal rules for doing so (within 3").