By default most plans come with 1 or 2 artist profiles included. The Label plan has slightly more with 10 artist profiles included by default.
Often 10 artist profiles just isn't enough for a label and that's why you can add more artist profiles to your account for a small fee that is taken every year.
You can add as many packages to your account as you want. In theory, if you wanted to manage 100,000 artists you could!