I haven't ever had to work under a review number quota system, but yesterday I read an aside that explained employer motivations for implementing them.
If you want to lay people off, you must pay severance/unemployment. If you require that x% of people must receive 1s, 2s, 3s, 4s, and 5s on their evaluations, then the 1s can be fired after an "appropriate" period for "poor performance." Being fired for poor performance costs the employer nothing.
So it's a % layoff with no responsibility taken