I mean, "just kill somebody" might be the fundamental part of creating An Horcrux, but going real deep and picking a specific target to create a specific object as the soul-vessel might make the ritual work better, somehow? Like you gotta decide to kill somebody for your own benefit, as a particular act of premeditated Evil Magic, that's what a Horcrux is; but the details might affect how the magic works. Maybe killing a total rando you never even learned the name of makes it much easier to hide your Horcrux, like it's magically predisposed to anti-Divination protections; or killing somebody just because they owned the Object you wanted to use as a soul container makes the Container especially robust; or killing a perfectly innocent baby makes the connection to the Other Side more clear so you can come back faster / more easily, etc. I can imagine that going all-in on Evil Melodrama might make the spell better in some incremental way.

EDIT:
Thinking about this some more, the corollary to this might be that Voldemort might have made his Horcruxes worse in some particular way if he used people as Ritual Murder Victims for reasons other than, in addition to, being a Ritual Murder Victim. Using Harry (or Iris, here) might have made him particularly Vulnerable in some way, because he wasn't "killing an innocent baby for my Evil Ritual", he was also "removing a Prophesied Threat", the magic might not like that he's doing two things here, that he's not properly killing them only for the sake of the Dark Magic. Ditto killing Myrtle because she was an inconvenient witness; it wasn't just using her as Ritual Murder Victim, so that might have introduced flaws into that Horcrux too.