It’s Basic Economics™.
For The System™ to be sustainable, when you buy a thing, you must receive less value than you paid.
value /ˈvalyo͞o/ benefit, usefulness, importance
When you pay $0 (Twitter/Facebook), the only way that’s sustainable is if they make your life worse.
I’m not making the claim here that “free” products always make everyone’s life worse (I’ll save that argument for another day). I’m just saying that the companies are actively trying to make everyone’s life worse.
It’s their only path to profitability.
“All profit-seeking businesses have incentive to provide as little as possible relative to cost. How is this different?”
If you pay $10 and get $5 in value, at least that’s $5. If you pay $0 all the company can do is rob you or inflict cruelty on you and charge others to watch.
The way this is usually discussed is “You are the product.”
While this is true, it isn’t specific enough. “You are the product” means that you are subhuman, beneath contempt. Any thought of benefitting you can only be in service of tricking you into less benefit and more pain.
This isn’t just bad for the customer, by the way. This is bad for the company, for the humanity of the people working there, for culture, war and peace, and the world at large.
“Free” products are simply the apotheosis of a purely extractive attitude in business.
The way out of this is clear: Charge the people who use your products for your products, and give them value: Make their lives better.
If you have a “free” tier, be sure it’s only ever in service of attracting customers to an honest exchange of value.
When evaluating any product, the first thing you should look for is where and how you can give the company money in exchange for the value they offer. If you can’t find that, run screaming into the night.*