It came down to preference. I find HyperApp's codebase simpler to read/reason about (it's a pretty straightforward single file), and I prefer its API over React/Preact's.

Because Preact and Hyperapp are solving slightly different problems.

Hyperapp is Elm-like state management (and soon effects and subscriptions in 2.0) on top of an ultra-lightweight virtual DOM diff engine.

Preact is a React 15 clone at best. Check out also https://github.com/NervJS/nerv for another React clone that is closer to React 16 (but still no fiber).