Voldemort may have been unaware of this possibility. Consider the following passage explaining why he needed Harry to retrieve the prophecy:
“Why?” Malfoy sounded incredulously delighted. “Because the only people who are permitted to retrieve a prophecy from the Department of Mysteries, Potter, are those about whom it was made, as the Dark Lord discovered when he attempted to use others to steal it for him.”
This tells us that Voldemort was initially not aware that only the subject of a prophecy could retrieve it. This is confirmed in one of Harry's sojourns inside Voldemort's mind:
“Avery told me Bode would be able to remove it.”
“Bode could never have taken it, Master... Bode would have known he could not... Undoubtedly that is why he fought so hard against Malfoy’s Imperius Curse...”
And confirmed again by Dumbledore at the end of the book:
“And then you saw Rookwood, who worked in the Department of Mysteries before his arrest, telling Voldemort what we had known all along — that the prophecies held in the Ministry of Magic are heavily protected. Only the people to whom they refer can lift them from the shelves without suffering madness.
Given that Voldemort's knowledge of how prophecies work was clearly incomplete/inaccurate, it is reasonable to suppose that he was also not aware that you could hear a prophecy by smashing its container. Indeed it would be expected that information about things in the Department of Mysteries would be top secret and not known to many people.
And while Voldemort did later confer with Rookwood, a former employee in the Department of Mysteries, it is possible that Rookwood did not tell him that a prophecy can be heard by smashing it – either because he didn't think that's what Voldemort wanted, or because he himself might not have known either.
