Interest rates have been low enough for long enough that many companies have been running on the “fake it 'til you make it” philosophy forever. Air BnB, Door Dash, Lyft, and countless others have never been profitable. But they survive by constantly taking out loans and collecting new investor money to increase their market share (the infinite growth scheme), hoping that they’ll either eventually have enough impetus to monopolize a market and bully it into being profitable, or get bought up by Google and co for a rich payout.
This is how YouTube and Netflix got profitable. They ran at a loss until they were popular enough to turn a profit, and then switched to maximizing that profit. I imagine the same is true for the big social media sites as well. Run at a loss until you have a big enough userbase to attract advertisers. And this is exactly why Tumblr was never profitable and Verizon basically killed it trying to make it profitable. Tumblr’s population has always been the groups advertisers like the least - minorities, LGBTQ groups, sex workers, and artists/creatives. So Verizon tried to sanitize it by purging them to make it attractive to advertisers, and consequently killed the userbase that gave it it’s potential for ad profits in the process.