There is nothing better than sharing a personal experience.
Short answer: replies and voting in live chats is pointless due to the speed of delivery and amount of information that is generated there.
There are two basic yet very important issues when it comes to live chat during streams: actually means.
As mentioned above a streamer has three tasks - content creation, content presentation and interacting with the audience.
However these three tasks have very different priorities.
And this is the first and biggest problem - how do you define something that in its nature is subjective?
In a live chat with video there are usually three big parties - the streamer (can be multiple), the moderator (can be multiple) and the audience: A good comment can be viewed by 2 out of the 3 parties as bad (obviously 3 out of 3 is best case scenario but it will probably happen 0.0001% of the duration of the whole stream).
The chances that someone goes through a chat history of over 100 000 messages and says "Hmm, message 458 133 seems like something worthy of remembering! There are many different communication channels used for their own specific purpose.
Chat is supposed to be informal communication between two or more people.
If we get a lot of messages and outline those somehow we can still create a large enough amount of such messages that it will become difficult to go through. A comment (like in a forum) is a much better way to ask for and respectively receive information on a certain topic. If you want important knowledge (good messages) to be preserved/outlined in a way, shouldn't their structure also be of good quality?
Adding an additional layer of interaction in such type of chat creates unnecessary overhead. *This is not research-based answer, but my own opinion.
Even if we know what good is what about the amount of messages and their speed of delivery?