I haven't played any of these games, but it makes sense in a couple ways.
For one thing, a prototype can suggest something compelling without necessarily delivering everything. I found this particularly true in the Limbo example. I found myself intrigued, thinking about the idea of a whole game that worked like that. It was strongly suggestive. But the reality is that it's just a short clip, the rest of the world doesn't have to actually exist. The ultimate release is likely to to make a variety of tradeoffs to realize the suggestions, which imagination doesn't have to worry about.
For another, a prototype only has to appeal to a limited group of people. The important part is selling or proving the concept. Customers represent a much wider array of tastes and while many will be drawn to a good concept, artistic elements are important too. If you're the sort that's more attracted to a clever concept than the overall experience, a prototype is more likely appeal to you in particular.
For one thing, a prototype can suggest something compelling without necessarily delivering everything. I found this particularly true in the Limbo example. I found myself intrigued, thinking about the idea of a whole game that worked like that. It was strongly suggestive. But the reality is that it's just a short clip, the rest of the world doesn't have to actually exist. The ultimate release is likely to to make a variety of tradeoffs to realize the suggestions, which imagination doesn't have to worry about.
For another, a prototype only has to appeal to a limited group of people. The important part is selling or proving the concept. Customers represent a much wider array of tastes and while many will be drawn to a good concept, artistic elements are important too. If you're the sort that's more attracted to a clever concept than the overall experience, a prototype is more likely appeal to you in particular.