git-bug try to improve over the previous iteration of this idea in several ways. To answer your question, those are what I think prevented them to catch on:
- it doesn't pollute your project: no files are added alongside your code, no mess during a merge, bugs are stored in your repository but decoupled from your code workflow
- it doesn't impose an interface: as you prefer, you can use the CLI tools, the interactive terminal interface or even a webUI. You could also integrate it to your editor, CI system ...
- it allows outsider of the project, client, users ... to browse and open bugs, without asking them to install anything. Admittedly, git-bug is not there yet, but the goal is to have the webUI work as a public portal that a project could host easily, accepting authentication from outside system (github OAuth ...).