1) I'm not generally in the habit of prognosticating all of the reasons a corporation the size of Google tries to do something, especially not when there's an apparent and obvious win possible from the change itself. Minimizing the URL bar leaves room for other things on the page, including chrome extensions and, possibly, page content.

2) UI improvements are not "cosmetic reasons," they directly translate to ease and efficiency of task completion. As a UI engineer, hearing my category of work called "cosmetic changes" can be, quite frankly, exhausting. If someone were to halve the default font sizes on all browsers, would we consider that a mere "cosmetic change" or would it be a change that would have direct and immediate impact on people's ability to accomplish tasks?

Well I'm exhausted by UI/UX engineers oversimplifying things that are inherently complex. To the point to not really helping people simplifying their work and totally hindering advanced user. There is a reason industrial UI usually don't suffer this, because complex interfaces are there for a reason.

You know what else is "a UI space resource hog" on the web ? Advertising. And I'm sorry but "wasted" space is generally much bigger. So, no, I'm not ready to loose my address bar for bigger ads.

There's a reason most commodity software doesn't adhere to industrial UI standards.

Chrome is well into the commodity software scale, and one should assume its UI decisions will lean in the direction of maximum utility for the most users.