The men are not yet cold under water, nor The bear half dined on the gentleman

The Winter's Tale includes a peculiar and oft-quoted stage direction.  (Exit, pursued by a bear).  It's a sort of bizarre non sequitur; no bear is present in the scene up to that point.  For context, Antigonus finishes a lengthy soliloquy lamenting that the task has fallen to him to abandon Leontes baby (yeah, that guy) whom he has rejected.  At this point in the writing of the play, one can only assume that Shakespeare asked himself "Well, fuck.  Now that Leontes has realized that he's totally wrong, why would he not interrogate Antigonus upon his return to Sicily, and go reclaim the girl?  Welp, guess I gotta kill him!"

And so the Bard expediently does so.  That's a thing, I think.  Expedience.  In The Winter's Tale, he throws a bear at Antigonus and drowns his entire crew with a aboardship.  Then he dusts off his hands and proceeds on with his play.

You see, the plot as it stands requires that Perdita be raised by a poor shepherd so that she can grow up and fall in love with Florizel, the son of Polixines.  The play takes a turn toward the lighter end of Shakespeare after this scene.  The madness and attempted infantcide are all out of the way, and it's time to get on with the mistaken identities, disguises, clever thieves and other madcap adventures one might expect in a Shakespearian comedy.  With just one problem... there are only two acts remaining.

It's really like two mini-plays.  Here's a quick tragedy; wherein Leontes fucks everything up, drives off his friend, has his daughter abandoned, and is responsible for the death of his wife and son; and now here's a little comedy that takes everything and makes it all right (sort of - Mamillius and Antigonus are still dead, after all).

But, I digress.  This is about expedience.  Antigonus death (and Mamillius's, his is even more offhand) are written in quickly in order to fill the playwright's need.  No words or time are wasted, nothing to see, just move along, we've got a story to tell.

Frequently, this is where Shakespeare brings in the supernatural:  the Ghost of King Hamlet isn't needed to draw Hamlet's suspicions, but his nature makes it possible for Shakespeare to say, absolutely, "this is so, let's move on".