Adobe Acrobat Pro, Foxit Phantom PDF. I'll concede I can't think of a file manager though.
http://dopus.com/ not exactly subscription, but you buy a major version, and each new major version is a new purchase.
Ultimately - because the person who owns the rights for the software wants to keep charging them and since it's their software they decide what is charged for it, end of story.
If it's not a good deal for you, go somewhere else. There's no point arguing about prices beyond that. There's no 'should' in prices - only what people want to charge and what people want to pay.