Some of 7, 8, and 9 applies. I might be more interested in speakers if I had a perfect room or the money to spend on treating a room to make it perfect, and tens of thousands more to spend on the speakers themselves and all of the other equipment required for a reference grade rig.
Headphones can provide that same reference grade sound (in their own way, of course) for less than 1/10 of the price. The room, furniture, and everything else that can interact negatively with speakers is totally out of the equation.
All of the best headphones currently in production sell for around $2K or less. That's enough for fairly good monitors, or half decent floor standers. Reference caliber monitors are roughly $8K-$30K, and reference caliber floorstanders are about $15K to nearly infinity. Plus they weigh hundreds of pounds, and many are extremely fussy about placement.
If you can't afford to drop the price of a BMW 5 series on your stereo, headphones start making a lot of sense.