Currently, people have to prepare money and anything before they traveling and a bit of risk of getting mugged aboard, so people have to be active to just buy what they need and travel back immediately, which kind of make the game interesting and exciting. If people can trade point aboard, people will just convert all their money into point, maybe goes afk for a week, thinking like hahahaha i'm safe bitch, then come back. Also, it will increase the amount of people who will stay linger aboard waiting to their target flower or plushy to restock.
In conclusion, making selling point available aboard will make this game soften and destroy economy, you are not that weak ass aren't you?