third person present tense

I come to you wishing you can help because I didn't find any aswers to this one : why is it that sometimes the verbs in the third person of present tense don't take an "s" ?
I know I heard it in a Bruno Mars song few years ago but I can't remember which one and I'm wondering again now because I recently saw this "When the rain falls it don't rain on a few but when the sun shines it don't shine just on you" I'm thinking the sentence is some lyrics of a song.
Thank you to those who will be kind enough to respond and I'm sorry if I made any horrible mistakes while writing this, please correct me if you find one.