Not only that, but the slides are JPG with horrible artifacts, and the text is JPG too, making it look bad and not be compatible with screen readers.
The HTML is an export. It's not what the software was really designed to produce. That said, I don't know if the quality of the slides is really any better in the native viewer.
They can be with
% mgp -D <dir> -E png <mgpfile>
:)
Defaults to jpg though.