Confused about Vocaloid concerts and promotions!?

I'm a bit confused about how there are so many Vocaloid characters, but only some of them seem to perform in concerts or get promoted a lot.

For example, I usually see the main group like Miku, Rin/Len, Luka, Kaito, etc. performing at events and concerts. But there are tons of other Vocaloids I've seen online that I've never heard about before, and some seem to have pretty small or niche communities.

I actually feel a little bad because I once told someone a character "wasn't a real Vocaloid" just because I had never seen her before😭

I know Crypton is involved in a lot of the concerts, but I'm still confused about why some Vocaloids get so much promotion while others barely appear at events or performances. Is it because of licensing, different companies owning them, popularity, or something else?