Just like how in Mountain View some Googlers live in the parking lot. It's not cause they think parking lots are hip, space is expensive.
In a high rent market like SF, a programmer's salary plus benefits and employer taxes (loaded labor) is about $200K. Open plans have an anywhere from 25% to 50% productivity hit from increased distractions and sick time (sorry, I can't look up the studies right now.) So while you might save $30K/year/dev going from offices to open plan in an expensive market, you will lose $50K/year/dev in productivity. Since those come from different budget buckets, and management never really sees the productivity hit, management thinks they've saved money and convinced people that open plan is "hip", "open" and "collaborative", when in reality most people are unproductive, stressed, unhappy and now despise their noisy, smelly and messy coworkers.