On paper anyone can list magic materials and say "oh that would be good for a rocket motor or spaceship". The assumption being that just because a material or technology has one good property that it will be good for all uses. To reiterate the GP's point, rocket science is hard and engineering rockets is even harder. Just because an alloy is "lighter and stronger" than another doesn't mean it is necessarily better. The ability to machine a material within particular tolerances is often as important if not more important as weight and strength. If your magical new alloy or composite material is too difficult to form or machine or is three times as expensive then it's not appropriate for the job. All materials are not good for all purposes. For instance, carbon fiber is light and strong but is not always appropriate for use inside the habitable volume of a spacecraft because it can absorb water and outgas VOCs. In a system like the ISS where water vapor in the air is recycled into drinking water, having your walls suck up water can be annoying if not dangerous.

Rockets are hundreds or thousands of individual parts operating at hellish temperatures all of different materials each with their own physical properties. It takes a long time to make sure those materials in that design not only work well but that you also understand that configuration modes of failure. Changing the material of even one of those components alters the parameters of the design even if only slightly. A lot of small changes can lead to large failures. Even if some new alloy ended up being perfect for rocket turbopumps it would still require a significant amount of testing to make sure it's "perfect" nature didn't affect any of the thousands of surrounding parts.

Rocket engines and spacecraft don't just appear because advanced technology to build them exists. It takes a lot of system integration to make a workable design. Research in advanced technology is fine but research and development in rocket science is also important. Rockets don't just spring forth from piles or advanced technology. Rocket science also works in the reverse direction. Trying to find a better or more cost effective material for motor housings or turbopumps might find a material that works really well for gasoline engines or turbojet engines. It might make a rocket half a percent more efficient but might make a jet engine on an airliner fifty percent more efficient.