Your explanation is correct for individual stars, but it doesn't take universal expansion into account, which independently reduces the energy available from di

Your explanation is correct for individual stars, but it doesn't take universal expansion into account, which independently reduces the energy available from distant sources (apart from the 1/r^2 law). The reason? Same energy, more space, so a reduction in energy per unit of volume. Also, setting aside the issue of expansion and redshift, if you imagine a sphere with a uniformly illuminated interior (imagine a surface composed of so many stars that counting them individually makes no sense) and an observation point at the center, if you increase the radius of the sphere, there's no change in the energy received at the center. This idea works for an infinite plane as well, and is a bit easier to grasp. Imagine an infinite plane with a fixed optical brightness, and an observation point at some distance d. Now double the distance -- no change in received energy because the plane is infinite in extent.