Because players move. De Jong makes a blind side run and he's got acres of space to move into because Maguire was a good 4/5 yards outside to where he needs to be. AWB didn't get caught wrong side, he literally left the player he was marking, and I mean, he literally walked away. It wasn't a run, it wasn't a bit of clever movement, he was just left alone to do what exactly? He had nothing else he could possibly do.
Maguire is not covering Williams. If Williams gets beat then Maguire steps out, or, more likely, the CMs come across to cover. Because Maguire is out of position Lindelof steps forward and then AWB covers Lindelof. That's what defenders do. If one player gets caught out you shift across to cover. You get taught that in the u10s. Lindelof could have been more side on but honestly, he should be taking marginal blame.