1) Voldemort is the most powerful wizard of his generation. There's no indication that ancient wizards couldn't be more powerful, quite the opposite in fact - it's explicitly stated that ancient wizards were very powerful.
2) Voldemort was researching immortality, not the ability to bring the souls of others back from the dead. He's perfectly capable of raising armies of zombies however. Again, it's explicitly stated that he'd fear such an object, so there's not really much incentive for him to try to make such a thing.
If anything, Voldemort should have been capable of making his own improved version of the Philosophers stone, if he were truly as capable of making/inventing the best stuff along his lines of interest as you say.
3) The stone didn't really fully bring people back from the dead, making it as though they were alive again (which was actually what the stone was supposed to do). In fact, the stone seemed to be fairly useless in that regard. It could put you in contact with the dead people you wanted, but they were still dead people. Not very different from ghosts, except that they had more substance.
Frankly, if Death gives someone a resurrection stone with the explicit purpose of bringing the dead back to life, I'd expect it to bring the dead back to life, not bring back their undead shades. This is more likely to be a failed attempt to cheat Death by a wizard.
4) There were many, many ridiculous artifacts in HP that completely blows something like "bring souls back to life" out of the water. Too many to count. Stuff like portraits that were essentially the people who they were meant to portray in two dimensions, and crazy levels of spacial warping was the least of it. Time turners were the worst. They handed them out to children so that they could keep up with their class schedules for crying out loud.
Honestly, I suspect the biggest reason why the stone wasn't as commonplace as many of the far more ridiculous objects in the setting was that the inventor never got to pass on his craft to anyone else. Possibly compounded by the fact that the inventor as apparently a wizard of legendary skill whose knowledge may as well have been lost in time.Now Harry Potter wizards do some cool stuff, because they don't have to worry about silly things like 'sense' or 'physics', but that's a bit too easy even for them.
It makes perfect sense when you consider how far more potent objects like the Time Turner can be commonplace: it's probably just because the knowledge of how to make one actually exists among wizards.