Colored sections above are completed parts of the SpaceX Starship prototype. Created by Felix Schland and fael097

The vehicles will be reusable and Space Shuttle crawlers would require massive lifting equipment to move rockets. Wheels that deploy would enable easier logistics for moving the heavy rockets.

This was highlighted by in Felix Schlang's at What About It? video.

Elon Musk also tweeted that the SpaceX Falcon 9 iterative improvement was slowed down to enable payload safety and crew safety work.

The SpaceX Starship improvement will not be constrained to slower development. Elon Musk is targeting a fully reusable orbital flight in 2020.

Elon tweeted that the progress in any given technology is simply # of iterations * progress between iterations