What would Skate 3 have gained with a bit more time investment?
What the time would have given it is the potential for more efficient coding (think larger environments, bigger cap elements, smoother/consistent animations, etc) and the inclusion of more features within the offline and online aspects of the game.

What does a game cost to be made?
This is completely subjective to the game being worked on. For example, GTA V took roughly 4-5 years of development, 1000+ staff members, and 250+ million dollars to create. Minecraft for example was roughly 2-3 years of development by 1 person (2 additional at various times and later a team of roughly 12) along with a budget of less than $50,000 (since nobody took salaries). Banished was in development for roughly 7 years, coded by 1 person, and cost under $5,000 not counting time spent. To create a game these days can be a very cost effective endeavor if you have the know-how and the time to spend with it. Many mobile games for example are made by roughly 20 person teams in under 6 months for under $20,00 (counting licensing kits, but not counting salaries).

Why do companies go bankrupt or fire entire dev teams?
It boils downs to time invested, budget allocation, unnecessary spending, and Gold Revenue (money made after game release). Many of the companies who go bankrupt severely overestimate the buy in of their product. We'll use GTA V for example: In industry cost per dvd/br of a game its around $12 which covers printing, distribution, licensing, etc. Now Rockstar has to sale these copies through a distributor at a reduced cost, then they are in turn sold to a retail establishment for more of a mark up (most games you buy are marked up 300%-400%). We'll say that Rockstar sells each copy to a distro for $30 ($18 profit for them per disc), the distro sells it to GameStop for $45 and GS sells it to you for $60. This means that for RS to break even on GTA V they have to sell 8.3 million physical copies. Last I knew they had sold just over 6 million physical copies out of the shipped 33 million plus this figure does not account for the Digital copies sold. From a money perspective they actually made 220 million in the first 3 months after release which is partly why they posted a 30 million loss that quarter. In the following 3 months thanks to more unit sales and in-game monetization they started to profit.

After GTA V was finished however you start to see people let go from the dev team and various associated teams. This sounds incredibly bad, but it happens with every gaming project. The people let go tend to be temp hires in coding, art, music, and other less core departments. This will fill a gap of 20%-40% of the initial work force. *IF* the parent company is looking to maximize profits even more they will sell off the associated studio or simply close it's doors. Sometimes a rival company will make an offer that can't be refused just to close down the competition. When I was working with Z-Axis Ltd we were bought out by Activision and shutdown almost immediately. This way THPS and Mat Hoffman games had no competition from the makers of Thrasher and Dave Mirra. Business as usual, but shitty business nonetheless.

The same loss of personnel can happen if for instance GTA V had totally bombed. If the 250 million investment in developing GTA V had turned into the game only selling 100k to 1 million copies... You can imagine how many people would have lost their livelihood. If you want to see a prime example of not delivering on an investment that led to a company collapse just read up on 38 Studios. It is a festering pile of waste both on the company management side and government of Rhode Island side. Kingdoms of Amalur: Reckoning by them is still a damn good game and the MMORPG they were working on called "Copernicus" had a lot of potential.

Why are the majors pushing so hard to release games by a certain deadline?
Every company of size has a board that they answer to. These investors want to make money and if the company doesn't deliver then heads roll and money is lost. When a company comes across the "Golden Goose" game, then they want to seize upon it and milk it for all it's worth. EA with the Madden/FIFA/etc franchise, Capcom with Street Fighter, Activision with COD, etc are prime examples. As long as mindless drones will pay full retail for a slight bump in a game and at times a downgrade they will continue to fulfill your need. They could wait an extra time, but they might lose their window of opportunity to relieve you of your cash. If customers show restraint, then titles will slow down (or stop) and some companies actually have a thought that they want to make a quality title which slows the process down at times.

I mean once you have already purchased the equipment to create said game, what are you really losing?
I assume with larger groups like EA that they would already have that equipment.
Are you making back the money for physical copies?
The thing you are missing there is that they have all of the software/hardware needed for creating the title you like. Now that the initial heavy investment is out of the way they can just crank out game after game using the same formula for less investment. Using GTA V again if you think about the 250 million used to create new tools and such for creating the game... That cost is now trivial and when you make GTA VI and so on it allows for more profit which makes your heads happy with the bottom line. The issue that is presenting itself is that you are thinking from the perspective of a youthful gamer wanting to play the things he enjoys and not from the standpoint of a rich businessman who just happens to be invested into a company that produces video games. You want fun and enjoyment when you look at your monitor or tv and he finds the same thing by looking at his bank account. Rarely is a company investor, CEO, president, etc a gamer at heart because that tends to interrupt the flow of cash.

It's an annoying fucking dance between developers, producers, legal, finance, talent, and inspiration. I can count on one hand the number of people in the major industry I respect from a business & gamer standpoint.