It's not about the cost. Ability to reason with a blackbox can give insights into how it operates which translates into knowledge on how to bypass restrictions.
Fairly sure that's one of the reason for this. Had similar issue with Discord - removed the ability to add my Discord bot to new servers but refused to provide any reason or fix the issue. But unlike here, they said they're eager to see a new bot instead..
thanks - you’ve answered the question. this is how spammers would exploit such a service