For Facebook - I don't think forced subscription would work. People would be forced to think about how much they value the service (a less ubiquitous one at that).
1. Operating system 2. Programming IDE 3. Password Manager 4. Well I pay subscription for Netflix and Spotify but that's not really for the updates. Partly for new content, partly operating costs. 5. Facebook (I'd prefer to cover the operating costs by subscription, I really dislike ads) 6. Email - same as above
Also, actually I'd like all the services I use to provide feature updates now and then and continue trying to innovate.
Edit: also, if you do feature updates every now and then. Like it was with Windows or Photoshop. Then you end up having to support a lot of parallel versions with security and bug fixes which is wasted work really.
But - if those preferring a perpetual license were to be a strong minority, there would be no business incentive to make products in such a way.
This one is a total non-starter for subscription pricing. I'm not willing to use software that will potentially cut access to all my accounts if I stop paying them monthly.
Do you have any example of file managers or PDF readers with a subscription-based model?
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.
http://dopus.com/ not exactly subscription, but you buy a major version, and each new major version is a new purchase.