Why the JPEGs images processed through the Responsive Breakpoint Generator increase in file size?

When I upload a JPEG image, let's say 1920px and 200Kb, the one downloaded in the zip from the generator with same dimensions (1920px) is much heavier in file size, much more than the original 200kb.

Sometimes it also happens that smaller images are heavier than larger ones.

This always happens when I upload JPEGs, never with WEBPs

Why is that?