Why was Jack Kirby "The King"?

Because he didn't whine, he didn't make excuses, he "did it" better than anyone else on a frighteningly-regular basis!

(Look! "Kirby Quotes"!)

In a Bleeding Cool column, illustrator Kaare Andrews sez...

Let me admit that I’m not the fastest artist in the world.
It can take a long time to draw a page.
In the olden days, you had inkers basically ‘finishing breakdowns’ over Jack Kirby.
"Breakdowns" like this, which was typical of Kirby's "2-4 page a day" period (and he was writing the book as well)...?

From Secret Sanctum of Captain Video™

That’s how he could push through 4-6 pages in a day.
Kirby’s art was bold.
It was beautiful. 
It was awesome. 
But I’m not sure he would have as much success in today’s climate.
Which explains why Jack Kirby's art is used on so much of Marvel's licensed product output, and why sales of reprints of Kirby's work equal or exceed a large number of Marvel's new-material titles!
The truth is that the level of detail demanded on a page has risen dramatically.
Comics aren’t 10 cent disposable newsprints anymore.
They are a legitimate art form.
They always were a "legitimate" art form.
Ask any European or Asian art aficionado.
Paper stock is slick, coloring is high tech, and you can now print as many tones, in as many shades, with as much detail as you can imagine.
It’s expected from the fans.
Which "fans"?
Not me!
Must be the same "fans" who aren't buying the current output of Marvel and DC at even the same sales levels as five years ago, and not like 15 years ago, when I was working on-staff, and sales at 50,000 or below were a reason for cancellation, not celebration!

One other point, Andrews is an illustrator, not a comic book artist.
He's a decent cover artist, but his interior work is average at best, mediocre at worst.
Curiously, it also appears to be uncollectable or unwanted.
Every gallery I see online features his heavily-photo-referenced covers or pin-ups, not his panel pages!
Want proof?
Google "Kaare Andrews", then Google "Jack Kirby".
How many interior pages or panels do you see in each case?
That's why we'll still be celebrating Kirby decades from now when Karre is long forgotten...