People forget that modern 3D games take up huge amounts of storage space. Meshes, textures, maps, and sound recordings aren't cheap. You could mitigate this by

People forget that modern 3D games take up huge amounts of storage space. Meshes, textures, maps, and sound recordings aren't cheap. You could mitigate this by asynchronously loading certain files, or outright designing a game to be quickly downloadable (for example, by using an art style that uses only shading and mesh coloration instead of textures, or by going all demoscene and procedurally generating everything), but for anything resembling a modern "AAA" game, a long download time is probably unavoidable.