No matter how difficult the problems are - it still costs billions of dollars to develop a rocket program, and disposable rocket programs have the "advantage" for the industry of a steady order supply... which means the industry has no incentive to push for reusable rockets.

SpaceX has the advantage of being funded by a billionaire who isn't beholden to any political demands (including job creation/upkeep), and so they can do whatever promises the biggest profit.

I mean, if you have perfect measurements of the state of the rocket and a complete model of it then it's just physics.

Problem is that measurements are random variables and your model of the rocket is probably not perfect and now somehow you need to make it work.

Everything is "just physics"

That's true, I guess I was imagining more of a Newtonian approach, modern physics has everything.

Newtonian model gets you a rocket in a vacuum without atmosphere or vibrations made of indestructivle materials.

In the real world there is the atmosphere, fluid dynamics of the fuel, combustion stability, material science as engines have to withstand hot and chemically aggressive exhaust, etc.

It makes me think of the Laputans in Gulliver's Travels, the race of scientists that are so caught up in their theories they can't do anything practical.