Why isn't it?
The only better thing I can imagine is a single office. Closely followed by home office.
There is just one person you need to tell to be quiet in a small 2 person office. There are countless people you want to tell to shut up in an open office. This is also the reason so many people work with their headphones on. For some time I had those massive over ear headphones with me while I traveled through our offices. I didn't even listen to anything. Just put them on so I didn't have to listen to the environment. It's hell...
This can't get enough drama to become recognized as a problem.
An office with a door is IMO clearly the best option for most employees. I don't even really buy the collaboration argument. Every place I've worked that had offices had at least an informal open door by default policy. You shut the door if you needed to really focus on something or have a private conversation. But otherwise people felt free to wander by.