Our current era CPUs are only 64 bits.

Why has no effort been made to upgrade to 128 bit CPUs? Much less "1556" bit CPUs or "1556" Qbit quantum CPUs?

Such an upgrade would be trivial and easy to implement, as it would entail merely increasing the byte length of registers. So why have 128 bit CPUs not yet emerged?

Likewise with ASICs. If it is possible to increase cryptographic function on chips, simply by extending the bit length of registers. Why have we not yet seen ASICs with registers that can hold a bazillion bits?

Think of engines in cars. If exotic luxury cars are known for their V-12 engines. Why not produce V-24, V-36 and V-48 engines if the goal is to produce greater horsepower and torque?

Can it be said that, at a certain point, simply adding additional bits or cylinders to CPUs and engines produces diminishing returns.