In Larry Niven's The Fleet of Worlds, he proposes that the core of our galaxy is exploding, causing a space-faring species which evolved closer to the center to race outward in avoidance of a soon-to-be galaxy spanning shock/radiation wave. Although the nature of their chosen space craft (their entire solar system) preempts their having to visit any other planets, I could imagine that other species from that same neighborhood might not be so lucky.
Using smaller and hopefully FTL ships those species might jump a few centuries ahead of the wave, and find themselves in proxity to our beautiful little planet. In such a case, many of the travelers might make a pit stop on Earth to...
refuel, rest, repopulate-their-ships, share-tech-with-other-refugees, locate the next pit stop planet, and enjoy Earth's natural beauty and human entertainment.
If during this time, we primitive little primates confiscated their star ships and forced them to teach us how to make some for ourselves then all of the refugees would be stranded on Earth until we catch up with their tech and can join them in their escape.