The brain seems to be able to remember the lyrics very hard, even easier than remembering the facts or today’s dinner content.
When you are remembering the lyrics, you are also remembering the melody and singing at the same time, so the brain will have a lot of connections to the lyrics. Repeating the same song can also strengthen your memory. This is a way of practicing. The rhythm of the song and the rhyming lyrics can also help you remember more familiar.
Finally, if you like this song, the brain will work harder to remember the lyrics because of emotional connections.