Hi there! Thanks for your question! To answer simply: interest.
Our numbers for contributors right now are only tentative, and can and will definitely change! If the amount of people who apply to contribute is low enough, we would be more than happy to shift into a free to join! However, if the amount of people interested in joining is as large as interest currently is, there would be no way for our team at it's projected size and experience to handle.
We are also taking into account the possibility of physical merch, which if we go forward with, will absolutely affect how many contributors we can take. We will be taking everything into consideration once interest check fully concludes, as well as when the rest of our moderation team is filled out.
We hope this answers your question ^^