I couldn’t disagree with @VidsFromAphone ! Maybe they use the cheapest bags they can find, which usually don’t survive transferring around the FBA fulfillment system. They also look pretty cheap, crummy, and dirty by the time they reach the customers. Sellers who take pride in the presentation of their products spend more.
We started using 2.0 mil poly bags, and ended up using crystal clear polypropylene bags.
At 1.5 mil they are actually stronger than 2.0 mil poly, and they worked perfectly. We sell mostly plush toys.