If the vCenters were collected through the vROps - vRealize Operations Integration adapter, they could not be deleted via UI; they must be deleted in VROps.
From vROps, delete the account created during the setup of the vRealize Operations Integration adapter. This will change the status from Active to INACTIVE
in the platform, and no data will be collected further for the vCenters.
The other option is to go to the Repository page, select the vRealize Operations Integration pack, and click Uninstall.