My best guess is that these abominations are made in order to adhere to some pre-made design that specified all the visual aspects without regard for the existing technology. If somebody gives you an export of a design made in Photoshop and says that you need to match it pixel for pixel, that design might not be readily implementable. Depending on the approvals needed, or the cost of hiring external designers, asking them to revisit the design in order to match the tech stack might be politically infeasible.

So instead of design being the intersection of form and function, design becomes entirely detached from the function.