I'm not buying that the switch to tighter pockets in any way explains slow play. In fact, slow play was just as big a problem 10-15 years ago when the pockets were much looser.
Slow play persists because it is tolerated. There is an old saying about pro pool and it is "give the players all day to shoot and that's exactly how long they will take."
As those who play on Mike Zuglan's Joss Northeast Tour know, slow play is not tolerated on the Joss Tour. If a match is scheduled for two hours and Mike sees that it is 3-2 at the one-hour mark, he will get in the players' faces and tell them to hurry up. He's the exception.
The WPBA had a nice approach in the 1990s and 2000s. If a race to nine was scheduled for two hours, if the players had not completed eight racks by the one-hour mark, the remainder of the match would be played on the shot clock, with a volunteer overseeing the match with a stopwatch. The very prospect of having to go onto the shot clock motivated the players to keep things moving, and not many matches ended up on the shot clock.
In a perfect world, at least at the majors, there would be a shot clock in every match (or at least in every Stage 2 match) but it costs money to have that many referees and shot clock operators, and pool operates on pretty small profit margins to start with. The chess clock solution might well work, but nobody seems willing to try it.
I agree with all those who suggest that the lack of a shot clock reduces the quality of the pro pool offering, making the game less exciting to watch.