The tragedy of the commons happened. The old situation had a few fatal flaws (mostly discoverability) that meant that new entrants could take almost all the oxygen out of forums by having a weird form of "mass appeal." It worked for a while, but the cracks are starting to show.
Unfortunately, I doubt that we can put the cat back in the bag.
a) new entrants can't exist ( Parler, Truth.. whatever ) b) the rules are so generic that they ensure given platform can ban whatever
And this is why people clamor for simple free speech slogan.
If this is how we understand it, then we do need free speech.