As we know, the intention behind Voldemort's Horcruxes was to anchor his soul to meaningful and rare artifacts and leave them in hard-to-reach places, defended by things like Inferi, the Gringotts defenses, or deadly curses. His spirit remains on the mortal plane when his physical body is destroyed, until every single Horcrux is destroyed, which would therefore have to be prevented at all costs.
The diary doesn't seem to fit this pattern. It was a plain, relatively random object, which wasn't guarded by anything at all. Sure, you might argue, but it was his first-ever Horcrux- yet he definitely could've retrieved or moved it to a secure location later on.
Instead, the diary was left carelessly unguarded, eventually entrusted to Lucius Malfoy in a plot which would have eventually resulted in creating a 16-year-old corporeal Tom Riddle out of the soul part enclosed within it.
But what's the point?
During the events of CoS, there already exists a 67-year-old wraith-like part of Tom Riddle a.k.a. Lord Voldemort, which was wandering around somewhere abroad. On top of that, there is absolutely no way Dumbledore wouldn't recognize this young Tom, considering the fact that he kept a close watch on Tom during his time at Hogwarts.
As we know that a Horcrux contains only the memories and personality of the person at the time it was created, this 16-year-old Tom Riddle can;t contain anything that is not already within the mind of the 67-year-old Tom Riddle Wraith Spirit.
If Tom Riddle's diary had managed to recreate his 16-year-old self by draining Ginny's life-force completely, what would this have achieved? How would this help the existing instance of Tom Riddle in any way?
