The simplest way I can describe
Hatsune Miku is that she is a virtual
pop idol, or a Vocaloid (singing voice synthesizer), though that might be a gross simplification.
Obviously
pop idols and their peppy music are a much easier sell than the absurdist crooning of a disaffected polar bear, which is why
Hatsune Miku and friends are basically household names, whereas nobody really remembers Kuma Uta.