I think that is a large part of it, I strongly agree.

However, I think there are two other factors that come into play that are very tough for people to vocalize when they are defending an open office.

1. Open offices are more appealing visually to a wider swath of people. Of course you can make either kind of office pretty, but there's something about humans that just really loves the wide open spaces.

2. Humans are social, we like to interact, even at the expense of productivity.

Personally, I prefer an office-per-team approach, so sort of a middle ground that allows for fast collaboration but doesn't require negotiating with 100 other people on the same floor about noise level, etc.