I think the simple answer is that there is no incentive for major studios to invest in a good movie that doesn't have a universal enough appeal.
Looking at it from a Disney exec's point of view. (Who now owns Alien and Predator) If you are going to throw a wad a cash at only 8 movies a year, you want to maximize the ticket sales. Adults will get nostalgic over a Predator movie, but they will also get nostalgic for Star Wars or Spider man, and so are their kids. The movie that parents need to get baby sitters for is going to lose out in ticket sales just about any day of the week.
The catch is, these movies don't even need to be well written to be successful. They just need enough hands on deck to keep them from failing.
For the forseeable future, the bulk of our movies are are cycle of comic book, CGI and adventure films that straddle the PG/PG-13 rating scale. The long treasured, less family friendly franchises are being reduced to cash-ins.
The ones that usually break the mold are made from outside Hollywood. Dredd was British, I think. Rambo, along with the other Stallone stuff like Creed and expendables, I believe that if it were not for Stallone being in the drivers seat pushing those movies, they would be dead in the water or terrible reboots at this point. I think Stallone produced a lot of that with overseas production companies as well.