Why are images exported with more weight?

When I insert an image that weighs 100k and then I download it in 1x and 2x, the 1x img is downloaded in low quality and slightly less weight, and the 2x is good quality but the weight shoots up. How is it possible that there is no change in weight and quality?

Another thing that occurred to me, is that sometimes when I insert a 200k image in Figma and then dowloaded in it’s 1x version, this one has more weight and poor quality. Why is this?