I thought of the same but I like Miku because she is so generic. The industry standard for babbys first favourite vocaloid. In the distant future, there could be a change that they will create Hatsune Miku Gynoid so if its super popular, then parts will be cheap. I would also like to point out that Hatsune Miku (or CV01) was one of the vocaloids that broke in to the mainstream and before you knew it, she was having her first live concert. Having such classic as Ievan polkka to become a one hit wonder helped to give publicity to Miku (not sure if it actually gave it publicity). Of course there were a lot more hit songs, all listed in vocaloid wiki. Thanks to Miku, corporations saw the potential to actually make money out of these and started to invest on some other stuff around miku such as MMD software. I'm not completely sure if it went like that but you get the point.
Other than obscure reason, I'm constantly exploring new vocaloids to hear their voice if it were to have a bit different tone. The idea that you could create a song, more or less, anonymously using electronic instruments, software and with the help of Vocaloid is quite remarkable. You don't have to sing and by that way compromise your voice to malicious use. Vocaloid as an alternative to a human singer sure is dystopian view, don't you think? However it will happen, sooner or later.
Currently I do explore other vocaloids, but I do like Yuzuki Yukari and Megurine Luka the most currently. I don't have anything too rational explanations to back up why I like those two.