I'm not sure why they have done it but the provider I use has hundreds of thousands of users & when people vote for a feature it gets rolled out onto al users - I didn't know that you could still drag the images into the URL part but you carry on doing it that way then for the high res images all you do is the following:
Example - Full URL after dragging: https://static.wixstatic.com/media/70ebee_0f2eb20bfb9a489a88cfc4579027fdd3.jpg/v1/fill/w_682,h_309,al_c,q_80,usm_0.66_1.00_0.01/70ebee_0f2eb20bfb9a489a88cfc4579027fdd3.jpg
Example - Full res image:
https://static.wixstatic.com/media/70ebee_0f2eb20bfb9a489a88cfc4579027fdd3.jpg