eli5:with billions of stars emitting photons why is the night sky not bright?
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All of the “tiny angle of light emission hitting us means that we barely get any photons at all” is very true and valid, but there is another phenomenon that helps explaining even more such behavior: Red-shifting.
The mechanics of it are a bit rougher to explain, but it’s essentially that the ever-going expansion of the universe causes light’s wavelengths to lengethen so that over a long enough distance, what is blue ends up looking red, and what is red ends up in the infrared spectrum, which cannot be seen with the naked eye.
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