"It's the obvious, really."
ATP officials and tournament officials have been gradually and purposely altering court surfaces, especially at the majors, to make them so similarly slow and high bouncing in an effort to generate revenue, that as a by-product, they will indirectly finally produce a winner of the elusive Grand Slam of Tennis.
They initially decided to go with homogenizing that particular surface type because it creates longer matches and therefore generates more advertising revenue, period. Also, it takes less talent to play on a slow high bouncing court as compared to fast courts, giving them the biggest pool of players that can do well there, therefore making every match, even early rounds, potentially longer. It's much easier for talented fast court players to play decently on a slow high bouncing court, than the other way around. This all goes toward generating more revenue for each match, each tournament and majors most of all. Additionally, it was seen as easier and more cost effective to get rid of or change the faster playing surfaces, like carpet, and grass, since those were in the minority anyway. The acrylic hard courts only need a new coat of paint with sufficient mix of sandy grit to create a slow playing surface. Clay courts already fit into the plan.
The by-product of this purposeful homogenization of courts is that it is the quickest way to produce a winner of the Grand Slam (it is redundant to say Calendar Year Grand Slam (CYGS), because a Grand Slam means winning all the majors in a single year). Tournament officials have long recognized that good players have the ability to win a single major on a specific surface consecutively over 4 or 5 years. It is much more difficult to produce a player with sufficient talent to win on disparate surfaces during a single year and still be able to beat a player that is a wizard on a particular surface, which is why we haven't had a male winner of the Grand Slam since Rod Laver won in 1969 where 3 of the courts were grass and 1 clay (Roland Garros).
If all surfaces are made to play equally, it stands to reason that the best players on that surface type should have an easier time of winning 4 in a row during a single year, once they have sorted the alpha player out of the lot. A winner of a Grand Slam would mean even more revenue to tournaments. And they don't have to worry too much if top players get burned out or injured (continuously playing each other for long matches on a slow court) after 2-3 years at the top, because since all the surfaces are more or less the same, it won't take a great deal of talent to produce more top players. There will be some other top player that will easily come along to take their place.
They have almost succeeded already and are likely to succeed soon. Unfortunately for their plans, even though Mr. Roger Federer is extremely talented and therefore can play well on every surface type, he is at his best on faster/lower bouncing courts, which went against the strategic move toward slower/higher bouncing courts. Also, Mr. Nadal came along, who is exactly the type they wanted to excel. His problem is that he came along while there was still an extremely talented player like Roger Federer in the mix. Mr. Nadal's clay court wizardry cancelled out Mr. Federer on clay as did Gustavo Kuerten previously, and that's all it took to stop Mr. Federer from winning an amazing 3 Grand Slams. Mr. Federer was still able to win the other 3 majors in a single year, because the change has come about gradually and because of his prodigious talent. But as Mr. Federer fades, it looks very much like the best player types for the slower conditions are coming to the fore, and I wouldn't be surprised to see a Grand Slam very soon, probably as soon as Mr. Nadal fades. Will it be Mr. Djokovic? Perhaps, but he may have come just a bit early, and his injury free peak years might be over soon.
But again, a Grand Slam winner is a by-product. Their primary objective is to have long duration competitive matches during all stages of a tournament, for every tournament. I won't be surprise that in the future, after it is well recognized that all surfaces are playing the same, that they convince the tournament officials to all go to a single surface and type of balls. It will be the cheapest one to maintain, with characteristics that do not fluctuate greatly. They will use other sports as an example and excuse, since most other other sports are played on a single surface type.
On the downside, they will have destroyed what tennis purists would call the way classic tennis should be played, and with that, the history of the game. But those that are in power will say, "who cares about the purists and history, it's all about the money and the evolution of the sport". And as long as most of the average fans love gladiator type tennis where the last body standing wins, this approach is bound to succeed. Sadly, more knowledgeable fans or tennis purists unfortunately appear to be in the minority.