Firstly hi Fukurou, been a long time buddy
most studios noways have hundreds of people working on it, voice actors, actors for mocap, translation, hr, marketing departments, merchandise, renting the office complex, taxes and other legal costs, CEO buying ferraris, etc a shit ton of bloat. Game projects noways are less about making a game and more about making a multi media property, back then movies had tie in games, now games have tie in movies.
on top of that you have programmers and artists who are generally well paid, even for ubber generic slop art assets tend to be done from scratch and programmers always need to implement some new system to improve graphics by 1% that takes 100k lines of code.
no only that but this type of game tend to have a custom engine inside of a ready solution and even if they where to license a third party engine it is very unlikely that will feature some systems that might be required for the project, such as NPC ai systems, system to mix dynamic and mocap animation, facial rigs, side quest systems, Vehicle customization or some other laboriousness game mechanic. a ton of these can't be recycled from past games due to rising graphical requirements.
and even for licensed software it might cost a ton of money, if you have 100 guys that need a Maya license and it cost 2k a year, that would be a million dollars in just a license for one single software in a five year project.
yes even giga slop takes a ton of work