There are many problems with trying to have a conversation on Twitter.  

1. 140 characters can only express very simple ideas.  

2. Assembling a chain of messages is hard work. Storify helps, but only if someone is willing to put in the effort. For most things it's not worth it. 

3. Yogi Berra: "No one goes there nowadays, it's too crowded." For years social media experts have been writing columns saying the way to make Twitter pay is to "engage" with "key influencers." That means there's a lot of strategic engaging going on. In other words, spam. 

4. And Twitter has inadequate defenses against spam. How can you tell if the person at the other end is real or a kid in Guatemala or Malaysia being paid by the message to engage with people to help build cred for some spam-issuing Twitter account? And there's no way to delete a tweet short of blocking the person who sent it. So, as spam gets worse, the block gets wielded more freely.