Why are grocery store stock jobs so demanding?

Im from PA and i work at a grocery store called redner's. Well ive worked there for almost 4 years now and they start you at 8 dollars for 3rd shift which i work on and you only get a 25 cent raise once a year. My problem is they give us 1200 piece truck loads every night split between 5 workers and your obligated to bust your *** every night to put all pieces to the shelf and face and front all your aisles and then fill all the sale items. With all of that needing to be done in 6 hours cause it takes the first 2 hours to break down the pallets. Also the managers dont respect any of us on 3rd shift and always blame us for things being in the wrong spot and their 2nd shift kids never get in trouble for nothing. Im sick of us having to do most of the work in the store and we get harrassed about everything. Why is that?