People tend to ascribe a kind of cartoonish malice to things like this. I know Facebook more from the advertiser end than the user, and I this is my take:

The way adwords worked is that they put tools out there where advertisers can try X, and see what happens. If X works, they can try to do more of it. if not they can try something else. X can be the keywords you target, the ads you write, the bids you set, the landing page you use and a whole bunch for other settings. Over time advertisers got good at this. They got more out ads, bid against each other and the price shot up. The process took years and a qanta of advertising is still getting more expensive. The intelligence is mostly on the advertising side. Adwords is a fairly dumb toolset. The skill and experience of the advertiser can make a big difference to the ROI. The average skill level is pretty high in competitive markets.

They tried a bunch of push-button methods. They would have their "expert team" set up your initial campaigns or propose changes. I tried these when they were first launch with disastrous results. They also had more automated turn key management tools. They're also not as good as a decent ad manager. It's hard to beat a person for creativity and intelligence. Who would have thought.

FB adopted this model but their platform is very different. They added a bunch of hair at a rapid clip and adapted the adwords concept in confusing and inconsistent ways. The FB platform is more of a giant pile of tools, with 9 3/5 spanners and a hammer that can be used for a drill. This might be a little unfair. The gist of search advertising is pretty straightforward. Show this result to people in this area searching for this thing. FB is a lot more complicated.

Anyway… They built up an ad platform that is enormous and opportunity loaded for a lot of kinds of marketing for which adwords doesn't work. Are you looking for pre school enrollments? Promoting a comedy club? Daily dela site? Even the traditional orange juice and washing powder companies can fool themselves into thinking they are "engaging" customers. Anyway, FB advertising works really well for all sort of things. The demand is there.

The platform grew fast and no one really understand it very well. It changes fast and its confusing with multiple ways offing everything and lots of options you didn't know exist. There are lots of black boxes of the adwords adrank variety, but too many to easily understand.

But, underlying it all it seems pretty obvious that Facebook want to make their system much "smarter" than adwords. In an ideal world, you tel it what your goals are and the system chooses who to advertise to, how, when and how. More turnkey, less control in advertisers hands. Batteries include. Pick your metaphor.

Back to the topic at hand…

I think that changing how the platform works fundamentally is allowed in the FB culture in a way that is on the extreme end of the spectrum. The way I see most software is that a software metaphor is defined by what it does. If making something a "header" in a word processor make the text big & bold that's what "header" means. If "follow" in twitter means send that person a message and show me all his future posts, that's what follow means. I will adjust my behavior accordingly. If I'm following too many people, I need to unfollow some. If twitter thinks I'm seeing too many tweets, they can't just select tweets to show me. That changes the meaning of follow. To keep the metaphor intact, they should make the unfollow button bigger, or even suggest I unfollow some people.

Facebook would just look at the problem of too many posts, many commercial posts or similar and show fewer. Maybe they internally rank your friends and liked pages based on some black box algorithm and decide how many to show. Stuff like that. They're fine with this approach even though it means the definition of friend/like/etc. radically several times.

In FBs defense they serve one of the least savvy median user of any software in existence. I don't think that's an exaggeration. FB was a lot of people's first app.

In any case, I think this is just a manifestation of that core FB characteristic. Stuff changes in unusual ways. They have problems. Eg users who like hundreds of pages that would take over their stream. EG. my noisier friends drown out the occasional posters. The "normal" way of dealing with these things is to give user tools, controls or encourage them to use them. Unlike some pages. Curate your fiends list. The FB way is to decide themselves what stuff to show.

It's possible that FB is being motivated by "how to increase revenue" for these decisions, but I doubt it. It would be short cited and it can be explained otherwise.