He planned to secure them better once he realized the danger.
Until he learned that the cup was stolen, the Dark Lord thought his Horcruxes were completely safe, so until then he’d have no reason to choose to change how they were protected.
“Alone amongst the dead, he stormed up and down, and they passed before him in vision: his treasures, his safeguards, his anchors to immortality – the diary was destroyed and the cup was stolen; what if, what if, the boy knew about the others? Could he know, had he already acted, had he traced more of them? Was Dumbledore at the root of this? Dumbledore, who had always suspected him, Dumbledore, dead on his orders, Dumbledore, whose wand was his now, yet who reached out from the ignominy of death through the boy, the boy –”
- Harry Potter and the Deathly Hallows, Chapter 27 (The Final Hiding Place)
Once he began to suspect that his Horcruxes were possibly in danger, the Dark Lord immediately chose to go check on each of their locations and secure them better with more protection.
“But to be sure, to be utterly sure, he must return to each of his hiding places, he must redouble protection around each of his Horcruxes … a job, like the quest for the Elder Wand, that he must undertake alone …”
- Harry Potter and the Deathly Hallows, Chapter 27 (The Final Hiding Place)
However, by that time Harry had destroyed all but the diadem and Nagini, and by the time he got to Hogwarts, the diadem was destroyed as well, so he didn’t have anything to actually protect further. He planned on securing them further, but he didn’t seem to intend on gathering them all together. Doing that would be illogical since they’d then become easier to find if they were all with him. Having them in separate hiding places makes sure no one finds all at once.