The thing is that publishers and large developers have no urge to diversify their portfolios.
Instead of using that huge budget to make 3 or 4 titles of different genres/IPs, they instead pour everything into a single game and 'bet' on AAA status selling their product.
A game is either so huge, that it demands a gargantuan marketing budget or so small that it is a dumbed-down casual game. No one is interested in the middle ground and the thought that maybe having 3 or four unique titles, each earning from different market segments might be less of a strain than nothing but 'blockbuster' AAAs.
There is a huge amount that can be done with a moderate budget. If the Witcher 2 can get made for around 35 million, why the hell are companies pouring 100 million into a game that may or may not sell well based on nothing but the 'AAA' nametag?