Why didn't Voldemort just switch back to his old wand?

Question

In the final battle between Harry and Voldemort, Harry apparently wins because the wand Voldemort is using is actually under Harry's allegiance:

Harry saw Voldemort's green jet meet his own spell, saw the Elder Wand fly high, dark against the sunrise, spinning across the enchanted ceiling like the head of Nagini, spinning through the air toward the master it would not kill, who had come to take full possession of it at last.

And Harry warned Voldemort of this just moments earlier:

"But you're too late," said Harry. "You've missed your chance. I got there first. I overpowered Draco weeks ago. I took this wand from him."

Harry twitched the hawthorn wand, and he felt the eyes of everyone in the Hall upon it.

"So it all comes down to this, doesn't it?" whispered Harry. "Does the wand in your hand know its last master was Disarmed? Because if it does... I am the true master of the Elder Wand."

And we see that Voldemort did for a moment entertain the possibility that he was not actually the master of the wand:

"The true master of the Elder Wand was Draco Malfoy."

Blank shock showed in Voldemort's face for a moment, but then it was gone.

_{^{- Harry Potter and the Deathly Hallows}}

Now there was something very simple Voldemort could have done, and if there was even a slight chance that he would otherwise lose we would expect him to do this. He could have simply pocketed the Elder Wand and switched back to his old wand. That wand had never been won by anyone else so he could be sure of its true allegiance. And he wouldn't have to worry about anything to do with the connection between that wand and Harry's wand, because he knew that Harry wasn't using the phoenix wand.

So why didn't Voldemort just switch back to his old wand once he found out that Harry might be the master of the Elder Wand?

And if, for whatever reason, he happened not to have his old wand with him, why wasn't Harry at least concerned that he might have it?

Answer 1

Voldemort is arrogant

Voldemort is mainly arrogant, and ignorant. He doesn't understand how wands work, he likely just assumed that in order to win over the loyalty of the Elder Wand you'd have to kill the previous owner, just as he did with Snape instead of disarming him.

The Elder Wand cannot serve me properly, Severus, because I am not its true master. The Elder Wands belongs to the wizard who killed its last owner. You killed Albus Dumbledore. While you live, Severus, the Elder Wand cannot be truly mine.

Harry Potter and the Deathly Hallows. Chapter thirty-two: The Elder Wand

Thus, he could've assumed that Harry was lying, or that himself knew better than that brat child saying nonsenses, because Draco is still alive.

He wouldn't have time

While Voldemort's old wand would've worked in that duel against Harry, because Harry wasn't using his own wand since it was broken by Hermione, he probably didn't have the time to switch wands.

Let's guess that he would've tried to switch the Elder Wand with his old wand. Do you think Harry would just stand idly while Voldemort does that? Obviously not.

Answer 2

Because Voldemort don't know that, Snape was not the actual owner of the wand. When he killed Snape, Voldemort was under assumption that he himself is now the owner of the wand but in reality Harry was at that moment.

And You cannot switch your weapon in duel, by the time you change you are dead!!!

Answer 3

I don't agree with @Roberto, that Voldemort's wand would've worked because Harry's wand is broken. As stated in the citation in the question:

"So it all comes down to this, doesn't it?" whispered Harry. "Does the wand in your hand know its last master was Disarmed? Because if it does... I am the true master of the Elder Wand."

This does not mean the wand knows that it has been defeated by another wand, but by another person. So regardless of Harry's wand being broken, Voldemort's wand would recognize Harry as the one defeating his owner before (in fourth year, during the priori incident). So given Voldemort really did think about all of this and made a conscious choice about which wand to use (which he probably didn't, because he was surprised and acting out of the effect), this would probably be the reason.

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Another, off universe explanation, which seems far more probable to me, is that JK Rowling just did not think about it. As much as I love the Potterverse, it is full of logical flaws and things apparently not thought through. I guess for either Voldemort as in character, or for JK Rowling as a writer, the swap of wands was permanent and Voldemort's old wand just forgotten. The possibility to switch back just didn't appear to them.

Answer 4

Voldemort can't use his wand because it is ineffective against Harry's wand. The wands are too similar; they both have the same core. so this sets up a rare kind of feedback loop and their wands become joined by a single thread

The phenomenon is called: Priori Incantantem:

The Reverse Spell effect, otherwise known as Priori Incantatem, is an especially rare manifestation of this spell[3][4] that occurs when two wands with with the same core (that is, taken from the same animal) attempt to duel each other. The winner's wand forces the loser's wand to produce "echoes" of the most recent spells performed in reverse order

Priori Incantantem is a rare occurrence of Priori Incantanto:

Prior Incantato1 (PRI-or in-can-TAH-toh) Type Charm Hand movement Hold tip of wand to targeted wand Light Gold Effect Shows the previous spells cast by a wand [Source]

"A jet of green light issued from Voldemort's wand just as a jet of red light blasted from Harry's — they met in midair — and suddenly Harry's wand was vibrating as though an electric charge were surging through it; his hand seized up around it; he couldn't have released it if he'd wanted to — and a narrow beam of light connected the two wands, neither red nor green, but bright, deep gold... he felt his feet lift from the ground. He and Voldemort were both being raised into the air, their wands still connected by that thread of shimmering golden light." —Harry's and Voldemort's twin wand cores connect

And the Elder wand NEVER worked for Voldie because he was never the master of it. So he really needed to find a new wand altogether.