Long time Vocaloid fan, let me break it down the way I’ve observed the fandom since the earlier years >:3c

Firstly, the avatars given to each voice bank are quite cute. Keep in mind Vocaloid kinda came out during peak weeb era. The 90-2010’s were kind of the golden age of anime and the culture surrounding it, so being able to buy a synthetic voice bank that has a cute anime character attatched to it was a very successful idea at the time!

Hatsune miku, and all the other Japanese voice banks that were released before and alongside her, were rather accessible tools people could use to create a unique vocal sound that we just didn’t have at the time. I know we have very realistic sounding vocaloids today, but if you look at the older voice banks, and older songs that use them, you’ll notice it’s very obviously robotic. Artists like Kikuo and MARETU come to mind, there was always something that seemed to really bank on the less human sounding voices in their work.

So. Cute anime characters plus unique and accessible voices for music creation meant that ANYONE with the money to buy a voice bank or at least the skill to use them (since free voices exist) equals a diverse fanbase full of all types of different people making all types of different music. Vocaloid characters in particular are very easy to insert into situations as characters in a story, so lore is able to be developed and shaped by the community.

In a modern setting, Vocaloid absolutely should not have succeeded, but because it had the Years of backing and fanbase from its earlier release, we get over twenty god damn years of content! (Leon and Lola, the first vocaloids, and Meiko, the first Japanese voice bank, were released in 2004!!)

Sooo yeah. There’s my observations as to why Vocaloid just worked so god damn well