There may have been a point when specifically ATOS was running some sort of bonus system, but I suspect now it's got a lot to do with their targets as much as anything.
An ex assesor put up an interesting article about what happened when they tried to write up fairly and how reports were repeatedly returned to be re-written, and how that affected everyone's work load, and office popularity.
Which ever way you turn it around I'm comprehensively visibly disabled with records from birth and stamped 'unsuitable for adoption and fostering' because of it in childhood. That's before it got significantly worse later.
I was refused attendance at my local medical examination center (2 streets away) which was proud of their figures for refusal, as too complex. So quite why later a sports therapist was chosen to interview me, clean across the other side of London (bypassing many other centers) I don't know.
He was a terrifying nightmare, and refused to look at supporting medical evidence of why I couldn't do what he was demanding.
I made a formal complaint about his very aggressive behavior, and lies.
TBF once they realized I had the lot illicitly on tape, and just how bad it was, and frankly what he was trying to claim required a medical miracle that x-rays could immediately disprove, I got apologized to, and was encouraged to accept an immediate phone reassessment direct with a case handler, looking at the medical evidence as they talked to me.