Using a stepper motor for an electric bike
Well, yes, a stepper could be used. But why?

A BLDC (brushless DC) motor often has an on-board controller or driver for energizing each of the coils in the correct sequence and at the correct time. A DC voltage is applied, and it just works.

BLDC motors are most often optimized for medium-to-high-speed and medium-to-low torque applications, such as fans and servos. They do not have precise positioning capability; or in other words, zero repeatability (ignoring closed-loop servos.)

In contrast, a Stepper motor is similar to a BLDC motor, except without the on-board controller or driver. So you are required to provide the energizing current to specific coils, at the correct rate, and for the correct duration. A typical driver is something like this instructable, utilizing the ULN2003A driver chip, which makes design easier.

Stepper motors are most often optimized for medium-to-low-speed, and medium-to-high torque applications, such as mechanical positioners, paper feeders, CNC machining, robotics, etc. They DO have precise positioning capability (because you control each pulse which turns the stator.) Each pulse turns the stator a set number of degrees, based on the design of the motor. Common "step angles" range from 1/8th through 1/128th revolution. So very precise control of shaft rotation is possible. This is why they are commonly used for precision positioning applications, and if utilized in a feedback loop, have 100% repeatability. Their torque decreases as the rotation speed increases, however. So it would be more work to use a stepper motor, with little to no gain.

Here are some starting calculation examples to size the motor appropriately.