PGA West and Torrey Pines are typical Munis? Well, excuse me.. PGA West built in 1986 btw.
The longest course in my area when I grew up playing golf was 6800 yds from the tips.
http://brookwoodgc.com/about-us-2/scorecard/ And that was a beast.
The muni I played every day was a fine course and home to the local championships plays 6400 yds from the tips and it's already been lengthened.
http://www.fostergolfcourse.com/scorecard
Sure, the length of those courses are still ok but they weren't built assuming some fat ass puffing a cigar could drive the ball 280 yds. Back in the 60's and 70's anything over 200 yds was a big drive. Nicklaus used to hit the ball "250" and par fives were rarely hit in two on the PGA tour. You could make those courses a lot tougher by adding traps and hazards everywhere but that costs a lot money. It used to be distance was the equalizer for golf courses. What happens when drivers are hitting the ball 40 yards farther in 20 more years? Why did the R&A regulate square grooves? It would have been easier to regulate golf ball spin rates. Remember Sam Snead with his between the leg putter? At least they banned that for whatever reason right away and didn't wait 40 years to make a move.