But they have already solved the engineering problems (at least 10 years ago).

They already have "qbits".

The interface issues look to be 98% solved.

And the temperature cooling, the EM shielding, and everything else (that is outside the circuitry design and the physical chipset), a person with a budget of 80,000 USD can recreated in his garage.

Its the results I can't understand.

Why can't X qbits, in the time they stay coherent, produce results that agree with the mathematical analysis of the setup? Why is it always off by a factor so large that its not even productive for any task.

My understanding of it is not complete, this is why I ask. Is the interface issue only 2% solved (and not 98%), etc.?