Why arn't pci/agp cards produced the other way around?

I look inside my case from time to time, call me wierd :D Anyways is there a real reason why say graphics cards, everything is pointing downwards to the bottom of the case instead of upwards? Not only would it look much cooler for people with modded cards if the core/ram therefore fans and everything was pointing up, but its well known heat rises, therefore a lot of heat your card makes just sits under there. If it was reversed the heat could rise up into the psu out-take fans and cool down the case I would think.

The reason is the way the ATX spec sets up the slot alignment with the hole in the case. I've also thought it would be nice to have them going the other way. It might suck hot air from the cpu into the gpu cooler though...

It would be nice in some circumstances, but I think it could be a disaster for those of us with big heatsinks. Also like s1203372 said heat is an issue.. the GPU, CPU and northbridge would all be fighting for the same hot air.