Why there is no API to create user and user association?

Summary:

Why there is no API to create user and user association?

Content (please ensure you mask any confidential information):

There is a user case on our end that external system generates new user and user association info. Once that is done, since there is no user nor user association creation API in GTM at the moment (there is only a Get User Association REST API), IT staff who look after the source system have to manually send csvs to GTM support via email and ask them to upload manually. For us, this is an ongoing process day to day and it can get troublesome. May we know the thought behind for not having an user/user association creation API?