Because she is a pointless character who has nothing to do with Vocaloid except being a variation on Miku's design. Aka, she is a fanloid.
Whereas Miku and Teto have voicebanks, sure Teto's a UTAU but the existence of voicebanks makes a difference.
Edit:
Also, a lot of the time, Neru just uses Miku's voice for "her voice". So... If you like the Neru vocal.... You actually like the Miku vocal.
Except for the times Rin's vocal gets used instead.