SpaceX has numberous "firsts", including reusable rockets and some engine designs. So it's not right to say they just do things we've been doing for decades.
And on the other end, the physics behind fusion is pretty well understood. The difficulties/expense are in building the thing, and dealing with issues like plasma instability. We call that "science" mostly because it is a state funded project. If a private company were doing the same thing, it would be called R&D.
Interesting perspective. I agree that arguably most of the difficulties are more in the applied side of things, although calling it engineering might be going too far.
The big looming physics uncertainty is crossing the 'burning plasma' threshold, where the plasma becomes dominantly self-heating. There are two aspects to this: (1) will the plasma settle into a nice self-consistent steady state? (2) will the large quantity of fast fusion-born helium nuclei destabilize the plasma in an unexpected way? Theory says it should work, but the proof is in the experiment (which is why SPARC & ITER are being built).
You're putting the wrong construction on "too f'in' slow!!"
Technical difficulty is irrelevant to "too f'in' slow". If a technology is to make a difference now, when we need it to make a difference, it must already be deployed commercially at global scale.
Our menu of choices is: nuclear (fission), wind, and solar PV.
Better ones, driven by the government (albeit during a hot and cold war): the Manhattan Project and landing humans on the Moon, respectively.
Both had insane timelines, no clear or certainty of success but the pressure, backing and motivation delivered.
We need more of this, and yesterday.
But only where there would appear to be a benefit.
Fusion power generation will almost certainly operate like fission, in that it will need steam turbines, generators, elaborate cooling systems, and water treatment plants for the turbines and cooling.
The operation and maintenance on these alone is higher than that for wind or solar--never mind the operation of the reactor itself. The capital costs just for these modules are almost certainly higher too.
The project risk as seen by investors (delay, cancellation for social or undiscovered geotechnical reasons) is higher too.
So: generating electricity is not a use for fusion.
Fusion may have uses in scientific discovery. But a putative fusion power plant would operate well inside the limits of our knowledge, for reliability and safety reasons, so it would be no help there.
True, but the difference between too hard and only needing an organized push is often only obvious in hindsight.
I mean, if you look at both Tesla and SpaceX, nothing they've done was thought to be "impossible" from the outset from a scientific perspective. Electric cars already existed when Tesla was started, and we've been shooting rockets into space for decades. This isn't at all meant to minimize the huge achievements of those companies, but the science was never really in question.
Viable fusion is simply much harder.