@Dor: Because more often than not, I don’t sit down with a particular note to do prolonged writing; instead I cycle between different notes (sometimes somewhat rapidly), alternating between reading and making small edits. This makes having to frequently toggle between edit and preview mode (especially to see the images) already a bit awkward; introducing frequently switching to Typora would add even more friction.
Furthermore, for many people (myself included), visual consistency is extremely valuable. In Typora, my notes always look the same, which is very conducive to forming consistent visuospatial representations of the notes. By contrast, switching between edit and preview mode in Obsidian, and/or putting Typora on top of all that, is very disruptive in this regard.
As a consequence, I currently still spend most of my time in Typora, even though there are a lot of things I really like about Obsidian. If Obsidian had a Typora-like editable preview mode, I would jump ship in a heartbeat.