The open office plan is only there so that employers can control their employees. There is literally no other reason for it, it removes psychological safety which most people need in order to think while they are working. It allows obnoxious employees to create distractions in order to slow productive employees down. It allows clever employees to waste the executive function of people they don't like by flooding them with behavioral cues, gestures and body languages that has inherent meaning (This is particularly dangerous and devastating if done in a targeted fashion). I'm sure if you talked to a psychologist they could give you a million more fun games you can play with people in open office environments. They were never good for people to begin with or for getting work done. In small startups they are perfectly fine but in medium to large sized corporations they are only abused.

(BTW, none of the above bothers me in particular but I know this happens on all the time and I've watched people in large corporations play psychological games with extremely good employees just to make them miserable in open office environments.)