I understand that the difference in price charged in the market is much higher.

But, if I were to build a stepper motor driver and a stepper motor in China, versus building a stepper-based servo motor by adding a sensor and some smarts in the driver, the difference in parts cost is TINY. You glue a magnet to the shaft, put a SPI chip next to it in the enclosure, wire it up to the controller with a couple of feedback wires, and make sure the box has a small microcontroller in it. Done! In fact, the additional cost of the wires in the wiring harness would be the biggest expense.

If you want servo control with fancier motors, it will cost a little more, but BLDC / ECM motors are getting pretty darn close to steppers in cost (same amount of wiring, less iron, more magnets) and BLDC driver circuitry is approximately the same cost as stepper drivers (three output FET totem poles instead of four, so slightly cheaper!) Especially when you already have the sensor on the motor for servo purposes.

The future is absolutely servos. Steppers are relegated to $29 printers and such; they just don't know it yet!