Good question! I don't sell much but I generally sell on ebay, and I didn't want to sell it to someone who would break it by deleting the wrong files from the SD card, or update it to 11.4 one day and then come back complaining that it was no longer working. I know that if the person is reasonable you could explain to them how to fix it, but you could also just end up having to take return of the item, pay postage, and then listing fees all over again.
I did leave the firmware on a low version in case anyone wants to mod it themselves they can, that way gamers OR modders can buy it. There's no benefit to upgrading it to 11.3 and leaving no option for whoever wants it!