Corporate gigantism absolutely plays a major role in a lot of the budgetary waste that plagues modern AAA, but the ever increasing push for the use of new, more graphical intensive game engines and the accompanying need to create more complex assets with higher polygon counts and higher resolution textures and art assets contributes to spending inordinate amounts of money to end up with results that look marginally better (or no better at all) than games that came out 10 years ago.
And all with the added benefit of alienating more of the potential costumers and reducing sales because the new game requires a much higher spec machine just to run it because "MuH RoYtrOySain".
This is why I call it a graphical rat race, because it has become a pointless pursuit.