Managers, people in charge, rarely want to have objective independent measurement ... do not want transparency ... and do not want the associated accountability. Poor metrics allow managers to avoid accountability ... resources are consumed but good results are not achieved.
Example ... Development aid. Over 60 years there has been more than $1 trillion disbursed for development. This should have produced great progress ... but what has actually been achieved? Far, far less! Yet monitoring and evaluations mostly show that projects have achieved budgeted objectives. Please ... what is going on? All the performance metrics have been deeply flawed for years.
Objective ... independent. Data may objective without being independent ... but the system has got to be designed and structured so that this is so. Self reporting is a cost effective way of getting data ... but self reporting is notoriously self serving. However, a good system can mitigate the negative aspects of self reporting and make the data useful.
One way to do this is to have some level of independent data flow that will provide a benchmark against which self reporting can be checked. There can be internal check within a self-reporting system so that collusion is required in order for wrong data to be processed. There are other ways.