I agree that it does not take long when they are young, but sometimes it does not get done in a timely manner on some farms; apparently you have never bough replacement heifers that were not dehorned.

Not enough money in cattle to run them to the vet.
Our vet charges by the hour for all services and it is still a good idea to have a working relationship with the vet.  We have them onsite atleast 2x per year.  We have taken the occasional heifer to the vet to avoid a trip fee and after hours charge.

We bought some really nice yearlings with horns (price was right and they are good heifers) that will get showed so we had the vet cosmetic dehorn them, probably cost around $60 each, the ones that won't show cost $15-20. Ours were done while the vet was already onsite for Bangs, preg check, and herd health evaluation so saved the trip charge and the rest was by the hourly rate. Having a good chute and facilities keeps the cost down too.

Takes an extra 2 minutes when vaccinating if you goof off.
Zero extra time when using homozygous polled bulls and less stress on the calf.