The 1st major cost is salaries to employees, with the advancing hardware comes a higher paid developer to make content. If you have a team of 100 people all making 50K-120K a year, then you a monthly burn rate of up to 1 Million a month right there (don't forget about of those upper management types that earn the real the big money as well).
The 2nd major cost is your operating cost - the money it takes to keep the lights on, run the facility and operate the equipment. Building rent, energy costs, IT people... ect.
The 3rd major cost is the money you spend on software if you're not going to build the game engine from scratch. Unreal can cost 3 Million for one title if you want it to be royalty free from Epic.
Add all that together, and just over two years you got a game that is costing you 30 Million - and two years is almost nothing when you want to make a GOOD game, good games take time. 2 years of development can almost certainly equal a not-so-good game. Most AAA big name titles need 3-4 fours years, especially if you are creating original IP. Once set, pumping out a sequel on the same tech, same platform becomes an easy 2 year job with quality almost in the bag.
