Twitter as a private company can moderate content as it sees fit. But the government is supposed to be constrained by the First Amendment. And here, they technically are, because they're not forcing Twitter to take action. But there's always the background threat of regulation if Twitter doesn't play nice, so it's not as black and white as this.
Having been on the receiving end of such requests I was pretty happy all of them were made in a confidential manner, it saved everybody a ton of headaches and reduce the amount of grip the various miscreants had on our community. Doing that in the open would have caused massive issues, some of these people were downright dangerous and others simply needed help, keeping their data and our interaction around that data confidential was - in my opinion - a good thing all around.
You would have to decide on a case-by-case basis which requests can cause harm and which don't, which given the volume of such requests would add a fairly unreasonable burden on a company that was already cash strapped.
The only reason people want to know about this stuff is some kind of morbid curiosity. What you could do is to come up with a set of workable rules for which requests would have to be made public and which not, but I don't think I would be capable of coming up with such a set of rules that would not in the future lead to issues. So to default to secrecy seems prudent.
In that light, the sale of Twitter and the subsequent exposure of all these interactions presumably has the effect of such communications becoming more opaque rather than less resulting in the opposite effect of what you desire.