These things seem to have a cyclical nature about them. Prior to the ones that were built out in the hinterlands in the 90's, there were a handful closer in to town (North Richland Hills, Allen, maybe another I'm not remembering) that were either out of business or close to it. Now the ones built as tourist/roadside attractions are dying off and more are being built closer to town. Just seems like another part of the cycle to me. I hope I'm wrong. The one that opened in Grand Prairie a few years ago looks nice.
My understanding is that a lot of the stores that occupy outlet malls today are not true outlet stores in the original meaning of the term.
Originally, an outlet store was where a manufacturer or a retailer would sell overstocked, returned or irregular merchandise at a significantly discounted price in order get it off their hands and recoup at least some of their losses on it. This often resulted in very good deals for shoppers - so much so that such stores became extremely popular and had difficulty meeting demand given that there is only a finite availability of items which are genuinely overstocked, returned or irregular. And, when it comes to clothing, such items tend to occur most in the least popular sizes. So the companies with outlet stores began manufacturing/ordering stuff for the specific purpose of selling it through the outlet stores.
I am told that a lot of the stuff you see today in outlet stores was never carried by other retailers or the company's full priced stores - it is often a distinct line made specifically for the outlet stores. In other words, many of these stores today are little more than discount stores through which an established brand can sell merchandise targeted to customers who normally would not be able to afford their products. And by calling such stores "outlet stores" they are able to sell a wider base of customers without sacrificing the prestige of the brand name in the eyes of those who buy their full priced offerings.
That might perhaps explain the cycle that JBB mentioned (and this is just pure speculation on mu part). An actual outlet store (a good example of one that still exists is the Dillard's clearance store in Irving Mall and Six Flags Mall in Arlington) is of little threat to retailers. The reason the merchandise is there is because it was not successful or has minor flaws and is likely not to be available in all sizes. But a fully stocked store with brand name items at lower prices - that is a threat. Sure, maybe the line sold at the outlet store is of lower quality than the lines sold at full-priced retailers. But a lot of shoppers know very little as to how to determine actual physical quality of the merchandise they buy - many just rely on a brand's prestige and reputation as a guide. So it would make sense that retailers would pressure for the outlets to locate in remote areas - basically to add a "price" in terms of hassle factor to the discount stuff. And perhaps those outlet stores are successful enough that, when combined with the reality of online retailers, the pressure from traditional retailers to not locate in population centers is not as strong as it once was. Again - just speculation on my part.