Why do birds always nest in my garage?

In the words of The Carpenters, why do birds suddenly appear—seriously, it’s freaking me out!

For as long as I can remembers, birds (swallows, according to my parents) have nested in my (doorless) garage. I thought it was because we used to have those round light bulbs (like the one here), and they seemed more adept to nesting. At some point we changed to bulbs like this one, but they still come nest when they migrate.

Why do they always nest in our garage? It’s not like the birds that nest one year come back the next, is it? How long do they live? Would they remember where their nest was?

My parents don’t mind because they say they “bring good luck”. I (and my car) disagree.