I was looking how a servomotor works. I realized that a standard servo can only turn up to 180°, but I didn't understand why. Is it because of the potentiometer?
Fundamentally, because the systems they were designed for convert rotary motion to linear, typically with a range substantially less than 180 degrees (probably more like 120 degrees).
Next, because the control scheme of PWM position pulses is not able to convey requests over an arbitrary range - the mapping of pulse width to position must be limited, and it is sensibly set up to map to something related to the useful range.
Because these limitations in task, a fairly ordinary rotary potentiometer of less than 360 degree range can be employed for position sensing.
Given that the useful range is limited, and the potentiometer relatively easy to damage by over rotation, the gearbox is typically constructed with a mechanical rotation stop somewhere outside the normal range of self rotation.