This one is for the ‘s’ sound (especially plurals) at the ends of phrases.
Thinking a question mark at the end of a phrase that ends with an ‘s’ does several things.
The ‘s’ sound itself is diminished in volume – and so is easier to synchronize.
The end of the phrase now has a physical lift to it, which tapers the end of the phrase. It also resets the interior of the mouth in an open, tall position, ready to sing the next phrase.
And, perhaps most important of all, a question implies a continuing conversation – even if the question is only in the mind of the singer. The singer’s intention to continue the conversation changes the energy and will be noticed – probably subconsciously – by the audience. We know when someone is not finished what they want to say. We can feel it.
The next sentence will respond to the ‘question’ and this drives the energy of the song forward.