Could it be that whilst they are more sensitive they also have a lower impedence and are more power hungry? I would have expected that to have made a big difference. It could also be some other things:

They are easier to drive so you can get them louder before things get edgy.

They make a nicer sound so you can enjoy them louder

They are voiced differently to the ATC's so that they attack the notes in a different way

All conjecture of course.

I've always found the better my hi-fi gets the louder it will go without me noticing, but also I don't want to listen to it as loud as I used to.