When exporting from one enviroment and importing into another subvars are not carried over.
This is as designed behavior. From our documentation:
section 10.4 of the Development Guide:
All objects can be exported except agents, agent groups, logins, and users. You must uniquely
specify any object(s) to be exported. For example, if you export jobs or process flows that use substitution variables, the variables will not automatically be exported. You must export substitution variables explicitly as their own objects.
You must also specifically export the subvars on their own.