In this configuration you would either need a hatch which adds more weight while taking away rigidity or a sloping trunk which is harder to seal and would likely cause visibility problems. If you have ever sat in one of those 2nd gen 'Stangs ('67 and '68 ) and looked in the rearview mirror even though you had a full acre of glass you couldn't see much, and every bodystyle change after until the 'Stang 2 came out got worse. You have to realize that mass produced cars are always going to be a compromise between economy (how cheap can we build it), safety (are we gonna get sued in this litigation happy society we live in
because someone is an idiot and wants to get paid for it), and styling (are people gonna want to be seen in this). That is the short list and I think they did rather well considering. I mean if we let bean-counters build cars we would be driving the blandest POS's imaginable, and on the same note if the design people tried to balance the books we'd all be riding bicycles.