Is it something like this?

For someone who worked at one of these jobs at Amazon for 3 years

Basic wage: X

Bonus Wage: Y

Total: X+Y

Under the new system

Basic Wage: X+Y

Bonus Wage: 0

Total Wage: X+Y

The net effect is zero but principly the value of the bonus has been reduced to nothing, after the loyalty of rhe employee and the benefits that come with that, have already been collected by the employer.

Seems somewhat unfair from that perspective, but they can do what they want I guess.