Totally valid point. In most cases, I think the layman will generally find an equivalently priced speaker setup over $600 sounds better.
Reasons that I can think that someone might still go with open backs are:
• Portability - You can move around your house or go running without leaving the music.
• Less dependent of environment - they basically sound the same in a small, big, or acoustically reflective rooms.
• Leak less sound than speakers - you can blast music without waking up your kids or downstairs neighbors.
• Better high frequency reproduction - whereas full sound systems will generally do better with lower.
EDIT: Added price stipulation to where speakers start to sound better. Agreed that if you're not willing to spend much and want to listen alone, headphones are the better choice.
Reasons that I can think that someone might still go with open backs are:
• Portability - You can move around your house or go running without leaving the music.
• Less dependent of environment - they basically sound the same in a small, big, or acoustically reflective rooms.
• Leak less sound than speakers - you can blast music without waking up your kids or downstairs neighbors.
• Better high frequency reproduction - whereas full sound systems will generally do better with lower.
EDIT: Added price stipulation to where speakers start to sound better. Agreed that if you're not willing to spend much and want to listen alone, headphones are the better choice.