The out-of-the-box BulkAction functionality is implemented in the scripted single section "pyMyProcessActions" which is not P7 UX-like, doesn't match with the other OOTB harness UIs and shows a poor UX in comparison to the P7 standard UI rules. Furthermore to customise this is only possible via scripting again - is this by intention?
***Updated by moderator: Lochan to add SR Exists group tag***
As Rawap alluded to, the "pyMyProcessActions" section was deprecated in 7.x, and replaced with the newer "pyBulkActionsWrapper" section. If you've upgraded your application to Pega 7.x from a 6.x or earlier version, your portals may still be referencing the deprecated section.
You can review a sample implementation of pyBulkActionsWrapper by logging in as the OOTB email@example.com operator, launching the CaseManager7 portal, and selecting "Bulk Actions" from the operator menu in the upper right.