Your section is not set to 100% width and because nothing in the section has a width, the section shrinks to the width of the image.
Your image only has a max width value. Max width only sets the maximum width an image can go to. Its a limiter and does not set the width of the image so the image is getting set to a lower res.
So when you set the max-width to 1420px, it will continue to scale at 100% width till it reaches that 1420px width and stops increasing the max width at 1420px.
Max-width and Min-width are limiters. They prevent a box from increasing or decreasing width after a certain point but do not affect the actual width of the box.
Width = real width of box
max-width and min-width = box width limit. (the box will not increase width past 1420px.)