Many middlemen play a numbers game to attract, both customers and candidates: "The most ads", "The most candidates".
In this vicious circle of the numbers war the interests of the candidate can sometimes be forgotten and their data stored and exchanged without their express permission.
Strong candidates don't feel they have enough control of the process and can there time wasted discussing vacancies they would not be interested in.
The side effect
Candidates develop an unwillingness to apply for positions through the recruitment industry as they don't feel in control. There are even examples of a candidate's current employer receiving their CV from an overeager, overworked recruitment consultant - the last thing a candidate wants to happen!
The standards we all need
Agents need to get permission from a candidate for each company they wish to send their CV and details to. A good practitioner will also delete candidate data after a handful of months of receiving it unless receiving assurances from the candidate that they are still seeking employment and wish to be represented.