Todd McFarlane gave an update on Facebook why he left Spider-Man after issue #16.
McFarlane goes into detail why he left which includes Marvel Editorial asking him to make changes.
McFarlane included the straw that broke the camel's back with Spider-Man #16 and a panel that had a sword in the eye of the Juggernaut that Marvel requested to be changed.
You can check out the original art below as well as the changed version.
"TODD...why did you quit drawing SPIDER-MAN?"
I get the above question dozens of times whenever I am at a convention doing a signing. And now that question is posed to me on social network channels too. So here is a quick answer (and story) to that question...
Around 1988, I and a writer (David Micheline) had been tasked to help put a little momentum back into the Amazing Spider-Man title from Marvel Comics. The book had hit a bit of a soft spot and the company was looking to get it back to the prominence they thought it deserved. At the time the X-Men and Mutant books were all the rage. Well, over the next few years David and myself did what we were hired to do and we got people talking about SPIDEY again. My art skills were beginning to mature and people were noticing the way the book was looking too. After a few years of this, I was getting the itch to become a writer. no because I thought I had anything important to say but mostly because it would allow me to write stories with characters who faced Spidey that I wanted to draw.
So in 1991, I decided to leave the Spidey book and look for another title where I could leverage my drawing skills as the reason to let me write. "If you let me write the book, and I am not very good right now, I bet you I can convince myself to also DRAW the book for you." So went my sales pitch to various editors. If you wanted the skilled artist TODD it would have to be in connection with letting the unskilled writer TODD on the book. Surprisingly, Marvel instead offered to create a new SPIDEY title (they had been thinking about that for awhile, not because of me, but because it would be their fourth Spidey title and they could have one come out each week). Thinking they were being a little foolish to let me write such a new project, I kept my mouth shut and simple said "Sure, I can do that." Thus came into being a comic titled simply SPIDER-MAN.
The book came out and instantly set a sales record (one that still stands today for a book with one author). The book was at the top of the charts and things were looking good. BUT...as time went by, the company began to slowly pull back some of the control of the book and began asking me to change things. At first I didn't mind, since this was a part of the creative process from time to time. But over time it began to become a regular occurrence and eventually on one phone call they asked for another change and I said to them "Look, I'll make the change or your staff can, but once this month's book is complete...I'm done. I'm going to leave the book." This last change was just the proverbial 'Straw that broke the camel's back." It was no more important or burden to me than all the prior requests. I just felt with my first child a few month away, that then was a good time to step away. Catch my breath. And play dad for awhile. (During that time away the idea of IMAGE COMICS began to percolate...but that's a story for another day).
Below are two photos. Both are from the page that they made me make that LAST change in the last Spidey book I ever drew (issue #16). The panel to look at is the last one. My original artwork, which still hangs in my office today, has a sword going into the eye of the villain Juggernaut. After some silly phone conversations they needed the sword to NOT be poking his eye. If you have that issue OR you buy it in the future, you will see a DIFFERENT piece of artwork in the printed version. What you are seeing in the photo is the unused panel of the page that led to me leaving Marvel Comics.