to go to a warmer or cooler place
The main reason is most likely relious-based bigotry.
They didn’t migrate. They were the crown of Spain.
Addiction
to survive
The same reason people would migrate from Europe to the Americas (separated by not hundreds but thousands of miles) in the 16th century: a better life.
PORN!
Unclean environments.
people are lazy
The Non-believers of Mecca (Makka) maltreated, insulted, and tortured the Muslims to such an extent that they had to migrate to Madina where they were offered refuge.
When people migrate the population that they left becomes smaller. When these people migrate to where they are going to that population becomes larger.
Because they enjoy it.
so people can learn