In my world, a Fae (spirit) can enter the human world at severely dampened power and will be injured if it spends too much time there. Faes are not dead people, they are forces of nature more than anything else.
What would motivate them to enter and stay in the physical world.
Clarification edit: Yes these fae do feel like humans, but love is a foreign idea of them as they don't breed the way humans do. Basically, they were forces of nature that got into a war with humans which ended with the humans taking the physical world and the Fae settling the spiritual world. I apologise for being unclear, I was referring to why a large number of them would want to come to the physical realm, rather than why a few would.