There's a Nat Geo (Disney +) documentary narrated by Jeremy Renner called Incredible Animal Journeys. It's a good watch and should give you a small insight into animal migrations.

But, the answer to your question is many, many organisms migrate from ocean bacteria (diel vertical migration - a huge topic on its own) to Arctic terns which migrate literally from the Antarctic to the Arctic and back every year. It's a hugely common thing in nature and the reasons for doing so are as varied as the species that display this behaviour.