Why can't I setup sub account to share my forms and folders?

Thank you for reaching support,

Please note that sub-accounts are only available with our Enterprise plan: https://www.jotform.com/enterprise/faq/

If you wish to share your form submissions, you may click on the share button:

I hope that helps.

Best.

Is this the policy changes? Since I have another 2 educational accounts started few years ago, and they works with sub-account.

Yes, for accounts that already use that sub-account/ sub-user feature, it is still available for those accounts.

But for new accounts and old accounts that have not yet used the sub user /sub-account feature, the sub-user feature is no longer available. You will need to subscribe to the Enterprise plan.