Downloading it from Big Fish

Hey Guys,
Why can't I download Nancy Drew as a trail on Big Fish games?
The only option they have is to buy it but I want to trial it first and if i just buy the game how do I download it?

You can't demo the game, but if you buy it you can just do the install game after the purchase and it will install it.

I did like this one, but I've only played about 4 of the ND games thus far.