Session 7 - Bilaal Ibn Rabaah(ra) - So was the reason Companions migrated was to escape persecution?

Bilaal ibn Rabaah(ra) "The Rock of Fortitude" Session 7 Bilaal(ra) and the other Companions(ra) who were freed from persecutors are still having problems with the unbelievers. Some Companions(ra) migrated to Abyssinia but Bilaal(ra) and others who were persecuted did not migrate. So was the reason Companions migrated was to escape persecution? What was the real reasons and wisdom why the Companions(ra) migrated to Abyssinia?