As a long time resident of the "tourist zone", there are several factors. I first came to Disney in 1985, and 192 was still considered "nice". By our next trip in 1991, it was getting worn, and by our last trip before moving in 1994, it was declining rapidly. The main problem is that the area did not and or could not keep up with changing expectations. The upper part of the low end market was sucked into the value Disney resorts. If I remember correctly, the moderate Disney resorts started opening in the early 90's, DVC in 1991, and the Disney value resorts in late 90's.
Some of the middle and upper market went to Timeshare, and or onsite. Some of it went to I-Drive, as has the business (trade show) market. Some has gone to the home rental market. Disney has, of course, done a phenomenal job of bringing more people in, and keeping them on property.
192 has become a vast wasteland of poorly run and poorly maintained motels. Some became transitional housing. Some are filled with sex offenders (
http://www.wftv.com/news/news/local/9-investigates-sex-offenders-living-motels-us-192/nWCLM/). There are some bright spots, such as the Celebration area and the new resorts planned, such as Margaritaville and the "ski" resort (
http://www.orlandosentinel.com/busi...y-ramp-xero-gravity-resort-20150211-post.html). Hopefully, these resorts actually happen, and land on 192 becomes valuable enough to tear down and rebuild. The Margaritaville resort is being built where Splendid China and a dilapidated motel once stood.
I would not say it's one thing. It's a series of things, avoiding the reality of change in consumer behavior, and not having a response to existential threats to an area's business are at the top of the list. As a resident of Osceola county and FL, I can tell you, there is very little forethought in government here. It's all reactionary, and tourist taxes can only be used for promoting tourism, as well as building arenas for billionaire sports team owners. Even when they try to do something, like the ill fated "Beuti-vacation" (I kid you not) of 192, it was a few trees and purple light poles (the paint peeled within a year and stayed like that for years) in front of the kitschy gift shop with the huge wizard whose crystal ball blew away during Hurricane Charley in 2004 and has still not been replaced in 2015....