There is no direct / indirect option in JTS / LPA at the moment to bulk archive project areas.

You could use REST API to achieve the same. Please refer the below link for more information.

Link: https://jazz.net/wiki/bin/view/Main/DraftTeamProcessRestApi#DELETE_project_area

One possible way to achieve the requirement is to have a script perform multiple DELETE operations as the # of projects.

Meanwhile, for an out of the box option in ELM; you can raise an Request For Enhancement (RFE) on the portal below.

Do include the use case, business impact to allow the IBM Product Management consider this feature for a possible implementation in a future release: https://www.ibm.com/developerworks/rfe/