Technically speaking dinosaurs are still among us. I had some for lunch yesterday. It was a native species of chicken. Seems some of them survived the big ol' asteroid impact and a big and a small ice age.
Just as chickens are still running their course now bred for specific characteristics, so are box loudspeakers. Reference has been made to materials costs et al. What we have to put in proper perspective is that technologically, audio is an industry that borrows most of this from other industries, dynamic industries. The ultimate cabinet or panel frame would be the fictional Vibranium from fictional Wakanda of Captain America shield fame wouldn't it? Extremely hard but capable of absorbing and damping all vibrations and impacts for defense. Until vibranium becomes a reality, the course hasn't been run.
Speed is required for resolution but if we look at it closely weight is only one factor. It's power to weight ratio that matters as this dictates not just acceleration but equally important deceleration. Boxes or specifically the air pressure created inside them that aids the latter.
Now let's talk size. You really do need very large panels to get the low end extension of a pair 15^3 subwoofers. The first part is physics. The second part is economics. Power today is cheap. This was not the case when stereo first took off and 18 watts was an embarrassment of riches and Alnico was the most powerful magnets that could be had but for a price. Back then you needed big boxes for bass and horns for mids and highs to get SPLs that can be had today with little stage monitors with high powered amps driving them the same way you could with a sub sat system provided they have high power handling.
So why do many of us have large box loudspeakers if small ones will do. It isn't about playing louder, that's for sure. It's about a) reproducing at a larger scale b) doing so with minimal electrical and mechanical stress that causes distortion which leads to fatigue which leads to a listening session that for lack of a better word, sucks. The very same reasons one would need and thus seek large panels.
The plain fact is that there are things box speakers do better than panels and vice versa. Thankfully this forum is populated with experienced folks so we can skip the enumerations both ways. From what I see now, box speakers have caught up to panels in what panels do best and may yet surpass them if the trajectory is maintained. It is panels that are making slower progress in catching up with what box speakers do well. The best panel systems still come with boxed woofers.