They do not.
They lock down specific, controversial threads in this manner when outsiders start making confrontational comments. AFAIK this was done because the racist vitriol proved impossible to moderate.
Reddit has huge "tyranny of the majority" problems and many communities spring up to essentially censor the speech of people outside of that community so people in that community can speak their mind without getting downvoted (I.E. censored) by the masses of Reddit. BlackPeopleTwitter has a system where all users that are not verified black users will be censored if the moderators deem it appropriate, which is perfectly reasonable. Is this racist censorship? Absolutely and yet it turns out that's not always a bad thing.
I find much of the discourse on free speech to be an oversimplification to the point of self-parody. I support the intentions of free speech but not a literal interpretation of what it means, which is just never censor anybody ever. That literally doesn't work and can't work, it's not a thing that's possible outside of a thought experiment, you'll end up getting DDOSed by speech.
I don't see how twitter changing ownership will change anything structurally at Twitter. Jack Dorsey started out as a free speech champion many years ago. The things people say cause real problems for real people and at some point the rubber meets the road. A large site like Twitter is at the mercy of the politics of the world.
Even stuff like "Twitter will comply with local laws" is a subtle concession to local censorship laws. Cracks in the facade are already appearing before Musk even owns twitter.