The recruitment process you describe there only deals with the applicants who meet the minimum eligibility. The process you describe seems not to qualify any of those applicants via any proctored tests or interviews. You are skipping or ignoring the examination process entirely. It's no wonder you are frustrated with unqualified preference-eligibles polluting your certs!
Meeting the minimum eligibility does not qualify anyone for the role.
Meeting the minimum eligibility only qualifies an applicant to go thru the examination process.
Preferencing and ranking begins only when you have assessed who is qualified via examination.
The "Certificate of Eligibles" is the final list of rated and ranked qualified applicants eligible to be hired.