Economics my friend, economics. Hunting in Texas is big business, with drought conditions, failing cattle price's, cost of feed, and upkeep on the ranch, such as fences, roads, buildings, etc, hunting is looked upon as a supplemental income for the land owners, and in many cases is the only means of income.
We learn early that there are several things you do not do in Texas, first, you never ask a rancher how much land he owns, second, you never ask a rancher if you can hunt on his property. Asking how much land one owns is kinda like asking, "how much money ya got in the bank." Second, a rancher might invite you to hunt his property if he deems you worthy.
Hunters themselves are the cause that many land owners will not allow hunting on their property. I have had hunters tear fences down, shoot cattle, leave trash all over the property, leave gates open, and bring others with them that were not invited. It only takes a few bad apples, and the pie is spoiled for everyone.
As for penned hunting, most of the ranches that have penned hunting consist of thousands of acres. A piece of land consisting of 4500 acres is eight square miles, (640 acres equals one section, one section equals one square mile) would you consider that a penned hunt? Would hunting in this big an area not be a fair chase?
As for releasing an animal for a hunter to shoot, I won't say it doesn't happen, but I have never seen it, and would readily condemn anyone you sells a hunt like that. Because an animal appears to just step out on cue most often is the result of good guides, long waiting, and the ability to start filming only when game appears. I know several good guides here in Texas that can put you on a quality game animal in short order, not because they are penned, but because the guide spends many, many hours observing the game, and know it's habits as well as he knows his wife's habits. These made for TV hunts require a lot more time and effort that most imagine, quite often a 30 minute air spot has taken a week or more to film.