If the phrase "Most people have net-positive utility" is rephrased as "most people don't actively want to not exist" it sounds totally unsurprising, and not nearly as positive as the original sentence. Moreover, it doesn't seem to be the definition most utilitarians use: For example, "It's okay to create people as long as they will have net positive utility" would lose all intuitive support if transformed into "It's okay to create people as long as they won't actively want to not exist, even if their lives are filled with suffering".
If the phrase "Most people have net-positive utility" is rephrased as "most people don't actively want to not exist" it sounds totally unsurprising, and not nearly as positive as the original sentence. Moreover, it doesn't seem to be the definition most utilitarians use: For example, "It's okay to create people as long as they will have net positive utility" would lose all intuitive support if transformed into "It's okay to create people as long as they won't actively want to not exist, even if their lives are filled with suffering".