New account applicants to give a reason why they want a user account

I am looking for an option to have a brand new user have to input a reason/purpose for using the system and submitting requests/creating their account/group. We have users who we do know their information, requesting to use the system/creating an account and we do not know why until we reach out to them directly. They may not know the type of group they are, so they select one classification from the beginning, then we need to reach out anyway because they did not provide the information needed. If we could have a reason field on the initial account creation, we would have insight into the user and not have to reach out.