The major league ballpark has really only one job that demands keeping an eye on the ball.
The hitter should, of course. And the catcher, too. But for them, watching the baseball is a means to an end rather than an actual requirement. The umpire? Close, but he has limited jurisdiction; he isn’t asked to track the ball all over the diamond. If he’s working home plate his eyes are peeled to call pitches, but he doesn’t have to stay fixated on the ball for, say, a tag at second base. And while managers, fielders and fans are all looking on with varying degrees of attentiveness, they’re generally watching the game, which is very often different from watching the baseball.