One at a time shall we? Ignore marketing costs for fun.
Bad Boys 2 was a sequel, that's one point. Secondly it underperformed with a huge star in it, it probably would have hit 250 had it been pg 13. Domestically it did 140 and cost 130 not including marketing. In other words, results like that make a studio nervous. Only with Overseas and dvd will it make a profit. Proves my point.
Troy? Cost 170, made 132 here, and will only make it with overseas and dvd. Proves my point.
Gangs? Cost 100(although that number is way low) It did 77 Us. Proves my point.
Matrices? In a huge franchise, Star Wars could be rated nc-17 and do 200 hundred domestically but it doesn't make nc-17 a safe bet. The last 2 Matrix movies cost 300 total, and made 420 domestic. Here they actually make some dough, if they didn't have to advertise. In order to simply break even, they need dvd and overseas grosses.
So in those examples you had one aberration that made money and it was a huge franchise. I.e. R movies are avoided because they are bad investments. The average R movie makes far less than your average pg 13. 6 Alien and Pred movies all r?
Predator 60 mill
Pred 2 31 mill
Alien 78 mill
Alien 2 85 mill
Alien 3 55mill
Alien 4 47mill
356 mill for 6 movies all R rated. Are you telling me as a studio exec that I want to drop (probably) 100 mill or so in a movie that has only done 360 mill across 6 films? Limit it to people over 17, and have no big name actors?, and a middling set of franchises? I don't think so.