Automatically accounting the user name in the "Assigned To" field while creating a Lab Request in RQM

This is work as designed. The request system is intended to separate the roles for requester and the request administrator. Only user with request administrator permission can assign a request to a lab manager to full fill. However, I do see your point that if the user has request administrator permission, we should allow the user to assign that on the spot. However, this is not a common use case.

You can also explore 'self-service reservation', which allows users with that permission to reserve lab resources directly without going thru the request system.