1. Obsidian imposes its own take on Markdown. For instance, why can't we disable "indent using the tab key"? It's so annoying to accidentally indent/quote text while pressing tab to do something like "accept autocomplete suggestion". Obsidian's response to users' complaints about this was not reassuring: https://forum.obsidian.md/t/option-to-disable-tab-to-indent/...
2. I had to install tens of plugins to give Obsidian the features I needed, which felt too hacky and unstable in the long term.
3. I don't want to learn a new set of keyboard shortcuts for simple things like expand/collapse the sidebars. You can customize lots of things but at that point, why not stay in your IDE (e.g., VSCode) and simply add Vim Wiki extenions?