And some 80% of that are retweets or replies, not original tweets.
Most people do not use Twitter at all. When they do use it, it is mostly read-only. When it's not read-only, it's most retweeting stuff.
You can't deny that Twitter has an outsized cultural influence, but the underlying reality is sobering. It's not a "speech" platform for the masses as no actual speech happens by the masses themselves. If the retweet button were to be removed, the platform would collapse.
It's not surprising that the masses don't post. You can't express yourself on Twitter due to the character limit, so all you can do is witty superficial takes. Threading and replies are a disaster making a structured discussion impossible. These two things alone make the platform useless for most speech purposes.
And let's not forget the sour atmosphere of extreme hostility, permanent outrage, bad faith discussions, smearing, doxxing, cancellations, the culture is terrible.
Back on point, I think Twitter has a far bigger problem than a free speech problem. There is very little speech and it excessively rewards the most unreasonable speech.