The United poster above you agrees with my views so I think you're letting your bias cloud your judgement too much. If the Mata one was a clear penalty, please explain why Ashley Young, the player nearest and with the best view, instinctively appealed for a corner? Do you think that suggests that Azpilicueta was "about 5 seconds late" or that he actually got a touch on the ball? At any rate, if your own player isn't even bothering to appeal for a penalty, it can't exactly have been clear-cut.
As I've already explained, the fact there were no United players near Willian is entirely relevant. The officials cannot tell if something is deliberate unless it is blatantly obvious, in Willian's case it was hard to call, thus you would have to consider the context of his handball. If there is no one around him and no danger and no advantage gained by handballing it, then logically one would assume it was accidental rather than deliberate, which is the only premise on which a handball is supposed to be called for. It's a completely different situation if a United player is closing him down and challenging for the ball because it becomes harder to presume the player's innocence.