Look at some of the other responses here, they give a hint. The core problem is lack of reuse, which means you expend one hugely expensive aerospace vehicle pe

Look at some of the other responses here, they give a hint. The core problem is lack of reuse, which means you expend one hugely expensive aerospace vehicle per flight, massively increasing per flight costs. Importantly, the optimizations for expendable flight actually drive you away from optimizing for reusability. Expendable vehicles tend to have fewer engines on the first stage, cheaper first stages, and expensive, advanced upper stages. The Falcon 9 intentionally places the majority of hardware costs in the first stage, uses a cluster of engines, and is thus more suitable for reusability (it's easier because landings are easier, it's more worthwhile because most of the hardware cost of a launch is in the booster). On top of that you have the fact that throughout the world launch vehicle development has traditionally been dominated by only a few major programs that were run by governments. That substantially restricted rocket development due to the bureaucracy and the different needs and goals of governments vs. launch vehicle customers at large (governments are risk averse, have big pockets, etc.) Additionally, launch vehicle development was heavily restricted as a practical matter during the Cold War. Launch vehicles serve as dual use ICBMs, and the first launchers were indeed repurposed ICBMs. Meaning launch vehicle development had very serious national defense and geopolitical implications, so you didn't see a bunch of "space launch startups" during the Cold War the way you see today (SpaceX, Blue Origin, Rocket Labs, etc.) Then there's the brain drain on aerospace technical talent during the Cold War as well. If you had the education or the skills to work on this stuff then most likely you were pulled into some military or government aerospace project since that's where the money (and the national interest) was. Engineers in the 1960s and '70s could have built reusable rockets if that had been the goal, but it never really was. Even with the Space Shuttle the priority was covering the political bases first (being able to serve the needs of everyone who was supporting the program and keeping it funded) and practical cost savings a distant second.