I believe this is expected - the Get Team Invite link is used for account creation, so if you have Enable Account Creation set to false, then Get Team Invite link is disabled. Does this help?
Our users prefer a team invite link which they can mail out to any users they need to join. Also it is tedious to add individual email and invite users in mattermost
You could share (via email or in a channel) a link to any channel in a team where you want to add people to, and they will be automatically joined to the team when they click the link.
On the left-hand side people can click the “+” sign to easily join any open teams.
For private teams, I don’t think there is currently a way to invite people except manually.