Have you seen how fast printers with stepper motors can get? They print benchies in less than 3 minutes. The bottleneck is not the motion system, it's either the hot-end or the part cooling. Also stepper are super accurate and very flexible. Drivers are advanced and can tune for torque, speed, sound etc. Collision detection and skipped step detection is also a thing.

In addition to the other points made… steppers maintain full torque even when it’s not moving, so it’s better at braking tool heads.

Also? Steppers have a higher precision to a servos higher speed and torque (but torque that’s not constant.)

Finally they have a better response time. This isn’t the speed, so much as the speed that control inputs are reflected. Imagine all the tiny wibbles a printer makes during infill, the changes in direction would be sloppier with a servo.

Stepper motors are considerably easier to lock in a single location than continuous rotation servos. When they are commanded to a certain position they will STAY THERE. This makes precise positioning considerably easier vs a continuous rotation servo, which must use a sensor feedback loop to ensure it stays close to where it needs to be. And any feedback loop will involve small amounts of extremely undesirable oscillation and movement about the target point...

besides. we can already drive steppers significantly faster than any hot end can melt plastic.

Cost is the short version, yes.

I don't know what kind of servos everyone here is talking about that are less precise than open loop steppers. Low quality hobbyist stuff, I guess? Proper servo motors & drives are the standard for good reason for robotics, industrial CNC machines, and pretty much everything else that needs powerful motors with high precision. Much higher power density, higher RPM (good for increasing torque with a gearbox), equivalent or better precision, plus closed loop control is a huge capability and safety gain.

That said, good, industrial quality servo motors are 1) expensive and 2) aren't made in small enough sizes to be comparable to the steppers on most 3D printers. Even the smallest industrial servo + drive I've seen is about 5x as big as the steppers on a personal 3D printer and costs $800ish. Obviously, both are deal breakers for a personal 3D printer.

3D printers are a fairly ideal application for steppers. The moving parts are small and light, meaning you both don't need a large motor and the danger of slippage is lower. Plus, steppers are cheap.

Just to add on to this, I understand the technical benefits to steppers, but surely a stepper motor could be given some servo-like functionality by simply adding encoders to the stepper shafts. You can get rotational hall sensors with diametric magnets for a couple bucks each. Even if you weren't using the encoders to operate the motors directly, you could use them for fault detection. An encoder with 10 bit accuracy could just about match the substeps of stepper motors for resolution.

Now, most of the time when a stepper gets out of, well, step, it's because something's gone wrong and you wouldn't necessarily want the printer to correct it directly, but simply being able to pause on a fault and record the fault' time and direction would make a big difference to troubleshooting.