Hatsune Miku is a vocaloid, which is essentially a digital instrument that does not only produce sounds, but also mimic words in several languages. Therefore the program is very popular to be used for making original music or remix existing music (such as OP’s example of MCR and Taylor Swift).
Beyond that, Miku has gone on to become famous worldwide as a “virtual idol,” where people pretend that she is a real, digitized person with a personality of her own.
