There should be an “Invite All” button for inviting all of your followers to a studio. My reasoning is because one could get tired of clicking the individual icons of every Scratcher that has followed you especially if you have 100+ followers. With the “Invite All” button, Scratchers can invite their followers to a studio in an instance!

https://scratch.mit.edu/projects/488716610/

From,
@KoralAnnakiCalamari

Hi! This is actually as intended - there used to be an “invite all” button but we found that it was far too easy to spam people with invites. We removed it to encourage people to be a little more thoughtful with who they invite to studios. See this thread.

Za-Chary wrote:

This feature existed in Scratch 2.0, but it was an extremely easy way for one user to create lots of notification spam for other users, most of which was unwanted. By removing this feature, users are forced to work a little bit to invite a large number of users.