[fuoqi]

>lack of incentive/competition

I wouldn't say that. There were many projects with reusable stages, e.g. Space Shuttle boosters were partially reusable and the Energia rocket had a variant in development with first stage boosters landing like airplanes.

And there were number of practical problems at the time as well:

- Computers were relatively big and heavy.

- Rocket development was mostly focused on improving efficiency via higher chamber pressure, meaning that engines worked on the edge of their capabilities, which is not a great fit for reusability. It's one of a good reasons why Falcon 9's Merlin engines have the simplest open-cycle design with a relatively low chamber pressure.

- Number of launches was too small to make reusable designs economically viable (i.e. your production line would be idle for too long). Even today this number is not high enough, this is why Musk focuses on projects like Starlink to create an additional "artificial" demand for launches.