Simple. Because PREFERENCE is not universal. It is NOT astonishing that everyone doesn't share your opinions and preferences. It doesn't matter if you imagine that an LED is superior. In the opinion of many it simply isn't. Your preference =/= objective fact. No matter how aggressively you argue your point the bottom line remains the same: it's a matter of preference, not objective superiority. Just as many people here have made compelling arguments as to why notification lights are INFERIOR. Their preference doesn't make those who disagree with them look stupid or crazy. It isn't astounding or incomprehensible. It's really very, very simple.
Maybe you should start a thread about why Apple doesn't need an LED on their phones.
This thread would be much better if there were more ideas being tossed around as to how Apple could implement some sort of similar LED/Moto X Active display functionality in the iPhones to one up the competition (which they like to do...).
Instead, you and others here insist on arguing for 20 pages. If you don't think it is necessary, don't join the thread. (As I have stated earlier, if you are absolutely offended that someone is insulting Apple, I have a piece of advice for you. Take a deep breath. Then think for a moment: Apple doesn't need you defending them. It won't tarnish their reputation. Their stocks won't drop because of a thread on MR. I promise.)