When you are unable to prove the issue wasn't a workmanship defect, also companies often eat these costs out of goodwill.

Furthermore, the warranty determination isn't free, either: in addition to the repair itself, some (likely multiple) employee's time was spent determining whether or not an issue existed at all, whether or not the issue was covered, whether it could be fixed, and facilitating the whole transaction.

Repairs also don't result in 100% yield. Depending on your company policy you might be eating the whole unit because of a mishap or just plain stubborn components/physical realities.

Repair fees don't cover all of the organizational moving parts required to actually carry out repairs.