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I can't see that having the bolts there would be any less effective than having them at the back.

Have you ever owned a Cinelli Alter/Integralter/Angel? The stem body is immensely stiff compared with the thin walled tube which wraps around the steerer. As kerley points out, you can generate a proper clamping force as long as the steerer tube fits precisely into the clamp bore, because you then don't have to move anything very far to generate the required hoop stress, but in my experience that fit would need to be of the order of a light interference fit to make it work. Meanwhile, you're bending the whole body of the stem to generate your clamping force, which is going to deform to front clamp, and then you tighten the front clamp to stop your bars from creaking and that feeds back into the hoop stress of the steerer clamp. The only way to make it work reliably across the range of steerer tube OD tolerance is to make the extension of the stem deliberately flexible from side to side, which is pretty much precisely what you'd try to avoid when designing a stem.

Obviously, the stem will be adequate, because it turns out that you have to try even harder than that to completely fuck up cycle component design to the point where it becomes unusable, as witness supermarket BSOs, but it will necessarily be less stiff than a well designed stem of equal weight or heavier than a well designed stem of equal stiffness. There is clearly a market for novelty stems where looks totally dominate the design over function, and this is one of those.