The tourney directors can't just decide. They need approval from ATP and they wouldn't get it for carpet at all (challengers maybe, but not above).
The main problem with carpet is the same as the general slowing down of the courts - cutting out the unappealing serve fests.
ATP knows that if every match is = to an actual Karlovic - Raonic indoors match, tennis will drop in interest big time.
They'd prefer the classical gladiators' encounters to the death almost (as Djokovic - Nadal AO final), which are more interesting to the general public.
That's all. Slow hard indoors is just this notch slower for the returners to have a chance and have a tennis match. Otherwise the majority of the shots in a match are services, which is honestly quite boring.
I believe Ivanisevic could be named "The killer of carpet". He has a great share for the slowing down process.
All good points. I remember watching matches like Sampras-Becker on indoor carpet when I was a kid, and while both were spectacular players, the matches were really not that interesting. Almost every rally was 1-3 shots. I know a lot of people have a kind of "romantic" idea of carpet courts and want them back, but I sure don´t miss them.
Having said that, the AO final between Nadal and Djokovic is just too much, the courts are so slow that no one even attacks the net anymore. That´s too much, tennis should not be primarily an endurance sport. Outdoor hard courts should be faster and should favor some attacking tennis, no doubt about it. But indoor tennis is much more interesting now than it was in the 90´s.