I believe most states have regulations on when/if the damage needs to be disclosed. Maybe this repair fell under this regulation. I would be surprised if they just voluntarily offered this info. Carfax has agreements with certain software vendors that automotive companies use. The dealer does not necessarily send to Carfax, it is the licensed software under agreement. So maybe they coded it in such a way that Carfax would see it and they did not want the buyer coming back on them.
For the record, I have no idea why they disclosed this. Only a scenario that would make it plausible. Other than just their altruistic view on sales. Which may very well be the case.
