If you want to eliminate the primary functional parts of a bike (drivetrain with gears, chain and derailleurs) and replace them with some other form of power transmission (belt or chain with no gearing or derailleurs), that gives the same feel of what you just tossed out… yes, it is really that hard.
You are asking for the same feel and response of a mechanical machine that is replaced with completely different components. There is likely to be some variation in feel, even in the best of circumstances. As this whole idea is essentially brand new, there will undoubtedly be some testing, building and refinement required. Something this complex doesn’t just happen and is rarely perfect from the first implementation.
An unrelated example is the simple comparison of the feel and function difference between a manual or automatic transmission in a car. We are only now getting to the point that an auto can match the basic feel (while still notably different) and improved performance (mileage and high performance) after many decades of refinement, from the smartest minds in auto engineering. Despite the relative simplicity of a bike transmission, this is still a massive task to undertake.
This perspective is purely about the technical challenge to making that substitution and ignores the practical reality of the economics that are essential to drive it and make it a financially viable product (which is a separate discussion, IMHO).