Release dates are chosen on when they think the most sales will be. For example: 2K released NBA2K15 at the beginning of October while sports fans are getting hyped up about the start of the basketball season. Lots of sales and lots of money rolling in. The servers were all wonky and there were plenty of bugs floating around in MyCareer and MyGM. If 2K decided to hold back on the release of NBA2K15 until early December to get the servers running functionally and fix all the bugs in MyCareer then there will be a SIGNIFICANT difference in sales because consumers are not as hyped up about the release as they would be in October.
Hype is built up for the game with trailers and publicity so everyone gets stoked for the game. When a game is delayed, hype and interest goes down. This already happened with Evolve. Evolve was one of the kings of E3 this year; everyone was all hyped up ?Oh man! The devs of L4D2 are making a new co-op shooter game!" But hype and excitement towards Evolve is down since the game?s was delayed. Delaying a game is a last resort because massive hype = a titalwave of money and sales, and delaying a game will cut hype while consumers focus on something else. ?Evolve? Oh yea, that?s yesterday?s news. Today is all about Dragon Age: Inquisition!? Delaying Evolve cut the hype for that game and with less hype comes less initial sales. And initial sales are the things that matter most. Quality of a product is important, but nowhere near as important as getting those initial sales by any means necessary.
If a publisher releases a buggy game, they get to keep all of the hype and keep all of the initial sales that they?ve hooked. Once those initial sales are made, then they can fix it the product to proper standards. It may not be consumer friendly, but it?s the way that publishers can make the most initial sales. With that said, initial sales means more chances for money on DLCs and all that stuff as well. Initial sales, pre-orders, and hype are where the money is at, and delaying a game will cut those things, which is why publishers will do their best to avoid delaying a game. Patches are the best ways for publishers keep their initial sales and all the hype whole while still release a game that?s of acceptable quality.
Your final point is how "releasing a broken product kills sales for that game?? Not true, unless the game is severely broken, and even then Skyrim was buggy to hell, but still made a killing. Heck, the OP of this thread was motivated to make this thread thanks to Borderlands Prequel and 2K broke the bank with that game. Seriously, DNF still made money and it was a trash game. Quality of the game is not important as long as it sells and delaying a game costs sales, which is why publishers prefer not to do it.