To the OP: because blind tests/DBT don't give enough time. I've said this many times before and it took me years of listening to realize this, but A/B testing has its limitations/deficiencies. It's good for discerning large or simple differences, but to really get a grasp of the subtleties involved, one has to listen over a period of weeks to months (preferably in the same physiological state, same time of day, so hormonal, sleep, hunger cycles etc. are kept relatively constant).
Humans have a bout a 4 second memory when it comes to audio. That is why DBT is not only great at debuffing the myth cables make a difference, it is also the best. (other than using scientific gear, which says the same thing. Said gear not only hears better than you, or even me, it hear better than all humans by a long shot.)
Assuming you're using sufficiently transparent gear, if you still can't hear the differences among cables, then accept the possibility that your hearing isn't as good as others or you're not as trained as well to look for the differences being discussed. You can stop spending money on cables, but don't try to convince others that they can't hear something just because you can't.
Really, so by which shaman were you trained to hear these differences? I would put bucket loads of money on my passing a hearing test with better results than you. You can stop trying to justify any point other than you enjoy wasting money on cables.
I've also found that not all cables make a difference, and the ones that do produce varying degrees. IME, headphone cables produced the largest difference, then ICs, then digital cables, then finally, power cables. Ofcourse, this depends on the gear used.
One other thing important thing to consider is that changing wire material reveals the greatest differences for analog cables IME. For example, switching from copper to higher quality copper isn't as audible as switching from copper to silver.
BTW, let me make it clear that the cable-induced changes we're talking about are *subtle* and shouldn't be focused on too much before getting the proper source, amp and headphones first. I've found some good cables to even make some gear sound worse if the upstream components were of low quality. A good wire benefits most from a good signal. (no pun intended?)
Let it be clear the change are indeed subtle, so subtle they do not actually exist, and are a by product of a human consciousness, just like colours.
