[irthomasthomas]

It is akin to Heinz trying to reuse and refill their cans of beans. Rocket engines are big disposable tin cans carrying very expensive beans.

[mikewarot]

Rocket engines are far more power intense than jet engines. Jet engines operate at over the melting point of their components for years thanks to clever design.

The fuel is quite cheap compared to the rocket that burns it.