I've often wondered this. When I was at Google (c. 2011) there was one dev on the Google Finance frontend, and he was pretty good - IIRC he did my ActionScript readability review. Maybe he left and whatever skeleton crew is there now is actively fucking it up?
I'm wondering if Google Finance is also a casualty of Google's campaign to kill Flash. Notice that they got rid of the Flash charting widget, and now there are no charts whatsoever on the home page, and a barebones static chart for individual stocks. Probably some edict came down from on high that you can't use that widget anymore, and there's nobody left working on the project to replace it with anything useful.
I've gone back to Yahoo Finance too.