Probably because people have other difficult to drive headphones and the Q701 just sounds better out of high powered amps. This has been my experience.
If we listened to all the technical "advice" here or the science guys, we'd be all listening to a K701 out of an E10 only or similar portable device. Who wants to do that?
The Q701 out of portable amps doesn't sound that good (despite being "properly" driven. My Airhead can drive it with ease, but it's just not the same.
It seems nobody has figured out why the K702/K701 is so hard to drive. Same reason nobody can figure out why the K501 is one of the most difficult to drive headphones. I think the whole power requirements of the K501 are a bit overblown.
I think I once read that no SS amp can drive the K501 properly. What non-sense!
Now, I don't always believe you need amp overkill, but the Q701 almost always sounds better without messing with the sound signature. If I use high gain on my Q701 I only need to put the volume at 40% on my Micro Amp.
I could probably blow up my Q701 if I wanted to.
I haven't been a believer that plugging in my KRKs or other easy to drive headphones will automatically ruin it's sound signature on higher powered desktop amps. People on here lately seem to think this is always going to happen, but I never had this experience.
I do however think many portables sound awful out of the E9. I really do think it's best for the harder to drive headphones. My DJ100 sounds pretty bad from the E9. Very bloated bass etc.
BTW I cringe everytime I hear someone suggest you should not use the Q701 with a desktop amp, but instead use it with an amp with a 1ohm output such as an E5 or E7. Have they even tried this?! That doesn't work very well. IMO the E7 is basically like an E5 with a built in DAC.
Could barely drive my DT-770 Pro 80.