Aside from the very much sung “why didn’t they use the time turner then”, there’s a bunch of “Why didn’t they stop Voldemort then” that could be inserted at various points of the story; when you consider that:
1- Albus had a spy within the death eaters in the person if Severus Snape.
2- In “the Order of the Phoenix”, while Voldy could take Albus 1 on 1, he retreated when more people arrived, implying they could gang up on him.
3- Sure they couldn’t kill him without the horcruxes, but another important plot point is that they have a magical prison, staffed with creatures that absorb your life force. Sure, Azkaban seems like a joke considering the number of prisoners breaking out of it… But in the case of Sirius he could escape transformed as a dog because they didn’t know he was an animagus and hadn’t taken the relevant measures, and the rest were broken out from outside. Certainly, they could hold Voldy with the right measures. Albus was monitoring Voldemort and the death eaters activity the whole time. In the first book/movie, he even had him within his school, unknowingly sure, but he knew Voldemort was likely to try and get his hands on the philosopher’s stone, and was just like “don’t worry, it’s well protected”, not even trying to set up an ambush, or to pursue Voldemort once he knows he was there.
Yeah, but that’s only really a trap is there’s a way to keep him from escaping. Voldemort escaped pretty easily; had Harry not been there, he could’ve tried for some time, figured out the trick and then just left to re-evaluate his options.
While not explicitly stated, it’s possible that that’s actually what he did: If he’d figured out Harry, Ron and Hermione had been snooping around and had found the room with Fluffy, Quirrel might’ve willingly dropped hints so that they’d check, let the music play longer than he needed to so that they’d know someone was trying to take the stone and he could lure them all the way down.