That isn't exactly true though. For example, the neural net models that are used today in various GenAI startups were invented in the 1980s. But we couldn't have LLMs "all along" because we couldn't store the models, the training sets, or do the training compute with the computer hardware we had at the time. Similarly with rocketry there many technologies that have only been available in the last 10 - 15 years that make Starship possible. A sampling;
First there are solid state inertial motion sensors[1]. Those combined gyros, accelerometers, and magnetometers that way just a few grams. Those bad boys weighed a couple hundred pounds in the Apollo rockets. We put the equivalent up in a $100 quadcopter these days.
Second there is 3D printing of rocket engine alloy, this allows SpaceX to 3d print a raptor engine[2] both faster, lighter, and without error than any engine we could have built before 2010.
Third was the development of fracking which created so much methane availability [3] that using it for rocket fuel became cost effective.
Fourth and fifth changes were three decimal orders of magnitude on the ability of computers to compute with a commensurate drop in cost, and with that an explosion the the ability to use high frequency radio to do things that used to be done by cable harnesses and wiring. (sorry no citation, general knowledge)
I can appreciate that it is really really hard to internalize how much as changed and improved since Apollo and can strongly recommend a trip to one's local science museum if you have one to get a visceral sort of amazement at what Apollo engineers did with the technology available to them at the time.
So it isn't accurate to say we could have had this all along, although if one of the 'big' players like Lockheed Martin or Grumman Aerospace had continued investing even after the 'Star Wars' program was cancelled I do agree we would have had it sooner than we did. How much sooner? Maybe 5 years? But it is important to realize that at that time (late 80's early 90's) they didn't know that the Internet was going to be a thing and so they didn't have a built in "market" for all of that launch capability. Even with Teledesic[4] which tried to go there, you needed someone who like Musk who was too ignorant of what "could be done" to push a bunch of really smart people beyond what they thought they were capable of.
[1] Apollo PGNCS --- https://en.wikipedia.org/wiki/Apollo_PGNCS
[2] SpaceX simplifies Raptor engine: Has it used additive manufacturing? --- https://www.tctmagazine.com/additive-manufacturing-3d-printi...
[3] The U.S. fracking revolution has caused natural gas prices to drop 47 percent compared to what the price would have been prior to the fracking revolution in 2013. --- https://www.brookings.edu/articles/the-economic-benefits-of-...
[4] Teledesic -- https://en.wikipedia.org/wiki/Teledesic