In the thread entitled “Why do cats’ and dogs’ eyes shine” posted here, the thread explains that the tapetum lucidum allows these animals’ eyes to shine AND then implies this is the reason these animals see so well in the dark. But, the tapetum lucidum REFLECTS light, thus it would exit the eye - NOT enter the eye. So, how does the tapetum lucidum help animals see so well at night? I don’t follow.
It reflects back through the retina.
The retina is in front of the tapetum. So some of the light gets absorbed by the photoreceptors, while the light that doesn’t bounces back off the tapteum for a second chance at the photoreceptors.
We don’t need one because we are primarily diurnal, and it would provide little benefit, but potentially be a detriment.
I can guess, but what specifically is the detriment? Does it make vision worse, having an extra reflection? Is said reflection distorted a bit? Does it make us more susceptible to bright light?
I’d always assumed we just never needed it, so any mutations that might have eventually led to a tapetum never developed. Or that it was a mutation that didn’t confer any advantage and died out–perhaps in whatever bottleneck makes human so similar.
I’ll have to look it up, but IIRC it distorts the image some. Light scatter? I’ll try to look tomorrow.
Cats and dogs have something like 20/90 vision - not necessarily solely for that reason. They’re also colorblind, which means they see fewer colors, but not black and white, despite what cartoons will tell you. Primates had different evolutionary needs.
If you look closely… not all of them have the same glow in their eye. Some have a bright white light, gleaming… Others have colored or a “not-as-bright” white gleam also…
You explained your own answer. They are able to reflect all light surrounding them back out from their eyes that constantly absorb it. I like to think of it as level of elite status in the domesticated animal world… The brightest whit lights are the “enlightened” ones 
This article has side by side pictures of what a cat sees vs what a human sees.
Interesting stuff.