You'll find the answer in the link you supplied.
Regulators of professional registers like the GMC can make DBS checks and submit evidence to the DBS (actually the DBS has no investigatory powers at all)
The VRCT isn't on the DBS list of professional regulators so at the moment it doesn't have these powers or rights.
Also you've got the fact that a DBS check costs more than membership of the VRCT.
