Only because there is a (probably accurate) perception that 1. performance indicators don't measure productivity accurately for developers. 2. they are game-able 3. they imply repetitive work such that as fits the metrics.

1 & 2 would obviously worsen an un-meritocratic system.

There is not a soul alive who would look at system that could get him a raise doing the work he already does and say no to it. If the measurements were accurate then you would only get objections from unproductive people. Since everyone objects including the good performers whom it would theoretically advantage then known inaccuracy is the obvious reason.

Also, if the measurements were accurate and people quit over it, then rather than being horrified you would be delighted that it was so easy to locate unproductive people.

Just as people who know a lie detector test is nonsenses will avoid it only when innocent, the reaction to KPI metrics is the opposite of what you'd expect.