Slack - add all members when creating channel. Number of users limit?

I'm admin on two Slack workspaces. When creating a channel on the first (3 members), it looks like this (after choosing name and description):

When I create a channel in the second workspace (14 members), it looks like this (after choosing name and description):

Slack claims this "Add all members" feature only disappears when the workspace has 150 users.

I can't find discrepancies in the settings. Any suggestions why this is the case? Thanks