Put another way conventional cameras work with cumulative sensors (at least for this conversation we can say they do) which record the total quantity of photons and their intensity being received in each spot. The shutter is the process of closing off light input and recording the data from the sensor. Technically there's an upper limit to how much light cameras can take in, which they'd asymptotically approach I imagine.

Your eyes don't work the same way. Each photodetector cell will send a signal when it reacts with a photon of sufficient energy (wavelength, intensity will increase the probability of reaction if im not mistaken) and send that signal to your brain. There's a lot of other complicated stuff going on, but at the end of the day your photo receptor cells are only so sensitive, and if light is below the threshold that will activate them, you'll mostly just get signal noise. This is true of conventional cameras too, but they are generally just tuned for a different purpose.

Animals with good night vision have highly reflective membranes behind their photo receptors to increase the probability of a photon interacting with a photo receptor, and often have different tuning on their whole eye optical systems that make them more sensitive, but also more likely to burn. There are always tradeoffs.