Thermal Distortion your loudspeaker most likely suffers from it. But do you care?

The interesting thing about Alnico magnets and compression is that some theorize that the particular sound of Alnico magnet speakers is that they are actually subject to more compression than other magnet types because flux density is lower under dynamic conditions when the voice coil is excited. 

If high efficiency speakers are so darned good, why did the industry move away from them? So electronics makers could sell more expensive Power? Methinks not.

@ieales 

The industry moved away from higher efficiency because its expensive, when solid state power became available. Sometime during the 1960s it became obvious that transistors were substantially less expensive than tube power. So with the less expensive power came speakers that were less efficient because (no surprise here) the speaker manufacturers could make more money. As tube popularity waned, output transformers and the tubes themselves became progressively more expensive; meanwhile solid state power got cheaper.

But prior to all that, the industry moved away from field coil to permanent magnets, not because permanent magnets were better, but because they were cheaper as well! In a similar way, CDs were cheaper than LPs on both the record side and playback side.

Whenever you see movements like this, in audio traditionally its always been about increasing profit. There are things that fly in the face of this a bit, for example some manufacturers have learned how to reduce thermal compression in less efficient drivers by proper venting of the pole piece, allowing for greater cooling (although things like that can be applied to higher efficiency too...); IOW they are trying to improve the product rather than make more money on it. But that sort of thing is rare.

The question was rhetorical 🙄

 I posted because I feel many over-fixate on known or obscure issues without realizing nothing is or can be perfect all is flawed. 

As Atmasphere described, cost was a big driver to higher power and lower efficiency.  But, it was also partly a result of the success of stereo.  When it was just one box, it wasn't quite so bad that the box was big in size.  But, when stereo came along, there was a big push toward making smaller speakers.  Smaller size meant lower efficiency, but, that tradeoff was now possible because the transistor made it possible to get more power relatively cheaply.