I use Markdown constantly, every single day, and I have tried multiple times to switch to RST and failed. Ultimately the reason Markdown works the best for me is that it gets out of my way. I can just type, I don't have to invest significant effort in formatting structures and can just write. This makes Markdown ideal for my primary use case, which is note-taking live during meetings, and because I already use it there, I also use it for writing blog posts, documentation, and most other document writing purposes. I will freely acknowledge RST is better for writing documentation and formal structured documentation, but the learning curve/barrier for RST is enough higher than Markdown, that it's not worth it for me to use both systems.