While this is true, in some sense it is also a feature and not a bug. You don't always want the whole world seeing what you're writing. While Discord doesn't offer complete privacy (unless you restrict access), it provides good-enough-privacy in the same sense that you don't have complete privacy when having a conversation in a town square, but it's private enough. A couple of people might hear what you are saying, but your conversation isn't permanently and publicly archived.

This has its disadvantages, as you point out, but it also has advantages. What I really like about Discord is the fact that people actually connect with each other. I have never meaningfully connected with anyone on Reddit. Discord enables human connection for two reasons: (1) you have a village-sized group of people, meaning you can actually keep track of individuals and your relationships with them and (2) since it is private enough, you can allow yourself to be more vulnerable.