AVRs keep gaining more features, in many cases at the expense of the amplifier section.
The trouble with the statement "operating within their limits" is that AVRs and most amps do not have peak or other indicators when its limits are reached. I know that I am likely to listen to a pair of speakers driven by a quality power amp louder than an AVR. Not because it can go louder but because it sounds better louder. Some Bluetooth speakers are too loud at 70 dB.
My brother-in-law's Revel F208 sound fantastic at levels that I consider very loud (mid 90 dB level) driven by his Parasound A21. He manages to get the amp hot on an open shelf.
Driven by the Outlaw M2200's, the F206's got harsh in the mid 80's. In this case, it may be due to the Class-G power supply.
So the considerations (as we know) are the speakers, the room, the listener. So my answer to the question "Why didn't they choose and AVR?" is because it did not meet their needs. AVR's can meet a person's needs but they will not meet my needs.
- Rich