Blame it on the Germans. Apparently some Germans took what had already been common in factories since the industrial revolution and perfected it for office environments during the 1950s. PHBs everywhere have been frothing from the neck ever since.
Interestingly, the 'advantages' section of the Wikipedia page for open plan offices simply states "This section requires expansion". That's it? Nothing? The collective intellect of the entire internet population, after so many years, can't even think of with one little advantage? I pity the fool who tries to put me into an open plan office.