Why is there listing image size difference between many sellers even within same product category on amazon which can be seen only using a laptop or a pc?

The original issue was noticed by sellers here

Link to the problem – https://sellercentral-europe.amazon.com/seller-forums/discussions/t/11fe9359-aabf-4863-90c4-9d20b81e8ea4

Another seller facing same problem – https://sellercentral-europe.amazon.com/seller-forums/discussions/t/e5cda8e63c99b93ad20434107f21eb02

Another instance of the same – https://sellercentral-europe.amazon.com/seller-forums/discussions/t/2d09b907-9ec6-489a-b3f4-a57cf40a81ce

Any product i list, even with 1500 x1500 72 dpi images results in the same small listings yet all my competitors having the same dimensions have much bigger listing images.

Can anyone tell me why is amazon doing this?