Fact of the matter is that some fans would attribute the lack of long term planning to the fact that no companies are in direct competition with one another warranting the concept of long term planning. I also will say that this isn't just about the WWE either as every company other than New Japan Pro-Wrestling. The booking decisions made by United States wrestling promotions nowadays is an indication of how the world has changed over the years. The reason I use that logic is because people today in particular young people don't have the attention span of the previous generation and a lot of fans look as wrestling as a joke more than a serious profession.
In my opinion, I think that the reason why long term booking has went away in the world of wrestling is because it allows companies to now change plans on a dime rather than having to work harder to make new plans. This is not my way of saying the writers today are lazy it's more the idea of that they may not have enough of a background in wrestling or certain people are micro-managing their companies a little bit too much.
However, there is a reason that Daniel Bryan's push to the World Title heading into WrestleMania 30 was amazing. There is a reason why Kevin Steen vs El Generico in Ring of Honor was the greatest feud in ROH history. One last one and that is there is a reason why the Invasion is considered such a flop and that is because it felt like it was rushed. But the first two have one thing in common and that is how long in advanced they were booked and how the patience in booking was rewarded. Those first two are the reason why long term booking does actually work if done right.