You're under the false assumption that the board is rectangular:
As you can see, the artwork would've had to have been made even smaller to avoid printing on the black area.
No, I know it's not rectangular. I've got a dissected SF2 card here. I've had it dissected for like a year by now. I was using it to experiment with HuCard ideas.
the label wouldn't have to be THAT much smaller without the hump, and could even overlap the black board part. I think the only reason the cut the end so that it was like \_/ was for cosmetic purposes. They went "oh hey we can snip the edges and hump it, and make it look shorter than it is. They could've just as easily left the thing rectangular and slapped a giant label over the entire thing. The black portion would have just been far more noticeably larger, and probably more prone to popping up from idiots being idiots with the cards.
I'm pretty sure the main goal of the hump was to provide more structural support for the "grabby/inserty" end of the card. Some people push down hard on the cards when sliding them in, and when pulling them out, so the hump serves to make that part sturdy and not bend in when some hamfisted gimp pushes down too hard. If they push hard with no hump, the board would eventually pop loose.
At least , that's my guess.
oh and that text isn't written on mine, so someone else did it.