I honestly laugh whenever I hear people still bring up those early social media companies as evidence that social media heavyweights somehow come and go. None of those companies ever came near the global reach of FB. A quick Google search gives a peak user count of MySpace of between 75 and 100 million, for FB it's 2.7 billion.
Those companies basically all existed before the vast majority of people were even on any social network, and importantly none of them had real-name policies initially. And the modern challengers you give all have some specific, much smaller niche, e.g. image galleries for Pinterest. There is simply no other social network that has ever challenged Facebook in the "connect all my friends and let me give and see life's updates" space.
First, there are countries where Facebook is de facto synonym for the Internet. Thanks to its marketplaces, groups, and events, there are places where much of the online economy is heavily based on Facebook.
Second, I'd argue that nearly every mobile provider in the world that offers zero-rating does so by providing access to Facebook's services either free of charge or at a much lower price than the rest of the Web.
Absolutely no other company in history had these two advantages over not just their social media competition, but the rest of the Web as a whole.
By any reasonable measure, that was "at the same time"; it wasn't so much one replacing the other replacing the next as three early competitors fluctuating until one won out.
None of those browsers ever came near the global reach of IE. A quick Yahoo search gives a peak user count of Netscape of around 80 million, for IE it's around 800 million.
Not that I believe for one second Facebook has 2.7 billion active individual human users. I've never even used it but I've signed up to about 10 accounts over the years, and everybody I know also has multiple accounts for various reasons.
In fact based just on people I know, I wouldn't be surprised if already most people are just using "Facebook" for messenger.
Plus, I think society as a whole is beginning to see the toxic ills of social media in general and will push back in a "retro" "back to the basics" kind of movement, embracing old traditions like community, family and friends in meatspace.
Facebook is a horrible company which hasn't come up with and original idea in years. It now uses its "sign in with facebook" button to see which apps people are using before copying them completely and leveraging its social graph. At this point its a parasite on the web that stalls innovation.
Feels really there is a lack of true creativity and innovation across the board and they're more being driven by feature FOMO than anything else at this point.
I hate FB, but I hate making such stuff patentable/copyrightable/unreusable/uncopiable even more.
Look at what instagram has become from photosharing app to an everything platform that has a horrible UX.
Nothing, in my opinion. The problem arises when a company is so large that simply implementing a good interface idea completely destroys the value of the original. The best example is Snapchat. Snapchat got big, fast, because its main conceit, while simple, was pretty unique. As soon as Instagram implemented it, Snapchat fell off a cliff, because why use Snapchat when you can just use Instagram?
What FB has been able to do is smooth out those up and down waves by acquiring challengers (Insta/Whatsapp). They tried to buy snap too but when that didn't work they just copied features and now also copying TikTok.
So I don't think they're subject to those equalising forces as has been the case previously (and which do still affect everyone else - RIP Vine).
But what makes this worse is the fact that Facebook hasn't been very vigilant about their privacy practises or political influencing on their platforms. And they haven't really suffered any repercussions from that. Which might embolden them and others to continue to do so unless something is done.
As a simple example, those 'new entrants' (can we really call any of those four new other than TikTok?) are all multi-billion dollar companies, but by quickly cloning the interesting features of those entrants Facebook probably siphoned off as much value from those entrants as they are now worth. In a world without Facebook copying them all four of those companies would have market caps that were at least 2x their current levels.
More to come are: Telegram, Discord, Houseparty, Clubhouse
Plus global competition from: Wechat, Weibo, Line
Social networks come and go. The space is a lot more whimsical than people think. Remember Friendster, MySpace, AIM. A new challenger will emerge every 3-5 years.