The shuttle was hardly reusable. Yea, the airframe was, but after the first launches NASA discovered how fragile it really was.

Had they taken SpaxeX's approach, they would've discovered those issues much sooner and been able to correct them instead of mitigate them.

What we're seeing play out is an Agile project vs Waterfall project.

Agile, as the name implies, enables small, early course corrections so you don't waste effort and get stuck with something you weren't intending.

We're also seeing the difference between private sector risk management vs government. (Risk isn't just "exploding rocket", but risk to the investment of time, resources, opportunity, etc).