VOCALOID3 is a separate package that YAMAHA made only available separately from the voicebanks. With the VOCALOID3 voicebank (like SeeU or Oliver for example) you receive a "mini-editor" for free. This however is not the "full VOCALOID3". The actual VOCALOID3 is 9800 Yen, which is give or take $127 USD.
Originally the editor came with the voicebanks in full, but YAMAHA changed this since people could, for example, ID Hatsune Miku by name, but not identify what the name of the software she was ran on. People knew the characters far better than the software. They originally tried to change this by creating characterless voicebanks (VY-) but that didn't go as well as originally planned.