수능완성 2회 27번문제인데요

when i started to see every product on the shelf as piles of the raw resources from which they were made , i began thinking about them differently and had appreciation for what went into them.

해석을보면
여기서 빨간색으로 표시한 they가 앞의 every product같은데요
every product를 단수취급한다면 they 가아니라 it 이맞는것같은데 왜그런지 설명좀 해주세요!
아 그리고 every product다음에 piles가 오는것도 이해가 안돼요 ㅠㅠ