Too difficult to do it right. And the benefit is perhaps not that great in every room.
Controlled radiation down to where the bass-system takes over shows significant improvements in different rooms and placements. Response is more predictable and similar. This gives a much better consistency of tonal balance between different rooms, and improves clarity in lower midrange.
Yes, it is more difficult to design, but then you only do the engineering once, to be able to make many loudspeakers. This is the future of loudspeaker design, we will see more speakers like this. This is one way to reduce some of the drawbacks with small speakers, and since small speakers are easier to sell and produce and distribute, such solutions will be favored.