This isn't just an Amazon problem. I've got a friend who worked at Wal-mart for a while. They give points against you for taking sick days no matter how bad it is. One time she got sent home for having some poison ivy on her arms and was still punished for it. Workers who have high points, but not so many to get fired get their schedules screwed with until they quit.
I mean if you are in the top 90th percentile nationally for taking sick days, then working you into the schedule would probably be a nightmare for managers. By reducing your hours, they are reducing the scheduling work that managers need to do. Also, It's likely expected that every employee has some points, but taking way more than everyone else is what this type of system is likely designed to catch.
It's not just reducing hours. For example you might start getting rotated around different shifts. They'll make your schedule as irregular as possible to encourage you to accrue points or quit. My friend saw this happen to several coworkers in her two years there. Towards the end her direct manager even asked her why she hadn't quit yet.
