Hello Johnny,
As I see, it all depends on the initial determination made aeons and aeons ago by each (type) of Buddha. It is recorded ,even, that those who were to become Buddhas were given this confirmation by several other Buddhas in stages as they enconuntered Them in previous aeons. (Why this is not the case also with Paccekabuddhas (if it be so) I do not know.)
“…sammāsambuddha, and even he hesitates to attempt to teach.” This is ‘the mind interfering’, but in reality a Buddha has no choice BUT to teach. So it is not that the Buddha decided to teach because Brahma implored him to – the role of Brahma there was to ‘remind’ him of his true calling, which HE himself had taken upon himself from the start.
As to why Paccekabuddhas can’t teach Dhamma, it can only be a matter of their gathis – just like a poet or painter who immerse themselves in their activity for the pleasure and satisfaction of it without ‘going public’;it is simply not’in them’ to do this.
I hope this helps towards further reflection
Metta