I see your point, and there is definitely some validity to it. There is also *some* validity to they way they do it.
Look at the Revel C205 for example. The oval waveguide has been rotated 90 deg. In terms of tweeter dispersion, it appears to be a bad idea.
But consider this: If they kept it oriented horizontally (the same as for the other speakers in the lineup), with its oval shape, it would necessitate even farther spreading out of the two woofers that flank the tweeter. And increased spacing of the woofers causes increased problems in off-axis cancellations.
Ideally the woofers should be as close together as possible. That happens with the orientation shown above.
So it's kind of a tradeoff between proper orientation of the waveguide in terms of tweeter dispersion vs. spacing of the woofers.
Ideally, probably best of both worlds would be to use a waveguide dedicated to this particular model, one that is oriented more correctly for the tweeter but not so wide as to space the woofers too far apart. That would require designing a new part, and the speaker would still be handcuffed by the flawed MTM layout regardless.