What @dgoyette said. With larger games you’ll generally have different locations, which you’ll want to organize into different scenes, and often use additive scene loading so you can have common elements in your game in their own scene so you don’t need to duplicate them across many scenes.
Also there is a hard limit on the size of an individual scene’s serialized file. For larger games again you get around this using multiple scenes or other segregation techniques. See the below thread.
But for a simple game there is nothing wrong with a single scene. For something simple I tend to just have 3 total scenes. A splash screen scene, a main menu scene, and a gameplay scene. But they could easily all be combined into one.