Many factors affected Circassian migration
We can also make broad generalisations about the push and pull factors: the factors which forced the Circassians to emigrate and the factors which encouraged so many to choose the Ottoman Empire as their new homeland
Russian invasion and war, forced assimilation in to the Russian Empire, mass killings and the threat of further massacres, economic pressure and psychological pressure to leave their homeland. They had little choice but to leave.
Circassian immigrants were accepted by the Ottoman Empire, they shared the same religion with the Ottoman peoples, they hoped for a better life. They had more trust in the Ottoman Caliphate to protect them. Only a few Circassians agreed to settle elsewhere in the Russian Empire.