A lot of it has to do with the way that people ingest media now.
Let's take the History Channel, for example. Years ago, the channel was made up of documentaries and other kinds of long-runtime content. A show that was less than 45 (60) minutes seemed out of the ordinary. Anything that wasn't a well researched piece on the impact or specifics of some historical event would never air on the History Channel, because it didn't fit the theme of the channel. Then, reality TV started getting popular.
Networks realized that people would be just as happy from watching 30 minutes of drama than they would 60 minutes of research and information. Shows like Pawn Stars and American Pickers started cropping up on the channel, and those got superb ratings. They didn't fit the overall feel of the channel, but they still fit the theme: history. However, unlike documentaries, they brought the average TV watcher's attention to the channel: people who sat on their couch looking for entertainment, rather than education.
For a while, the shows were still focused on the items that they would find. Pawn Stars and American Pickers were like Antique Roadshow, but with a more modern and friendly twist. At the center of the show was the items, with the people only there to highlight and showcase them. They also added personality and comedy, which made non-history-buffs start watching. With each episode, more and more people, who were there for entertainment, started showing up and drowning out the people that just wanted to learn something.
Soon, the producers of these shows started to catch on to the change in their audience. They started dropping the historical significance of the items as the central point of the show, while simultaneously pushing the people holding the things into the spotlight. Rather than seeing a lot of people going "Hey, this isn't the point of the History Channel!", they saw more people watching those shows. Now, when looking at the History Channel, one doesn't see History, but personality.
How is Swamp People history? How is Ax Men history? The answer is: it's not. History isn't the point of the History Channel anymore - it's entertainment. People aren't tuning in to learn about the progression of WWII, they're showing up to watch a fat guy try to fit in a car, that just so happens to be a classic. The producers don't really care about education anymore. They care about keeping people entertained, because that's what brings in ratings.
The internet is moving in the same direction. It's no longer about sharing information and experiences - it's all about entertainment. People don't want to learn, they want to be happy - just like news channels. A news channel can get high ratings, as long as they pad all of the bad stuff with a bunch of feel-good pieces, so they end on a high note. People are flocking to popular sites like Facebook and Twitter, because they supply them with the same type of content. They open a page, see some funny picture or video, feel good, then go on with their day. They don't care about the life of a dude in Iran. They don't care about the struggles of someone growing up in a poor Asian country. Those things are sad. People want to be happy.
Just like how the History Channel figured out that people don't care about history, web sites figured out that people don't care about information. They moved away from long-form content like blogs and articles to quick media like videos and pictures. A picture can be looked at and evaluated in seconds. A video can be viewed in a couple of minutes. All of the fat of reading is trimmed into something visually and emotionally appealing, so that people can digest it quickly and move on with their day. They don't care about set up. They don't care about development. They don't care about leaving a site with a decently formed opinion. . They don't care about reading (I'm sure many people haven't even gotten this far into this comment). People just want to spend a minute somewhere; get a feeling- no matter how well supported or formulated that feeling is; and go on to the next site.
That's why the stream was formed and works the way it does. Social media platforms realized that people want to see what is deemed "important" and move on. They don't want to dig through content to find what they want - they want to be force fed entertainment. Facebook realized that it could let people rate posts, then sort it by ratings, and end up with a feed that has what people think is "significant" at the top.
The stream ranks things by feedback, which isn't a bad thing in theory. However, the benefits of a feedback-based ranking system come at the costs of a population that cares about entertainment. In theory, it's supposed to take content worth viewing and raise it to the top. However, the general mass has a different opinion on what defines "content worth viewing". Someone that views the internet as a means of sharing information will think that a well written and informed blog post or article is something that needs to be shared. However, a person that is on a site just for entertainment is going to think a funny picture needs to be seen by everyone.
At the end of the day, both people aren't really right or wrong, because their values are different. However, one side's opinion is more heavily weighted, because they're the majority. In order to satisfy that majority, sites started creating streams to bubble popular content to the top. Since more people like funny pictures than they do blogs, funny pictures and feel-good pieces started hitting the front page of sites.
Sites don't want to go out of their way to satisfy the few people that like long-form content, because there's no money in it. As a result, the same low brow stuff populates most of the internet, while the more thought out and contradictory stuff gets filtered out by algorithms.