Feel free to add on or correct me if I'm wrong but my theory is Botpress is open source and can be tweaked in many ways to build sophisticated bots. While Manychat has some limitations. As such, Meta would be more likely to approve a more pre-defined system. They can expect bots that come out of Manychat to be of a certain type. But not for Botpress. I think at the end of the day they are both different systems it might be tough for Botpress to get Meta partner without being confined to certain restrictions. Just my thoughts haha