I mean, I can see why. People plan papers in many different ways. Not everybody plans their paper with an outline. For some people, having to make an outline is just more work. It's kind of unfair to force everyone to turn in an outline (unless you're actually trying to teach someone how to make an outline, in which case there shouldn't be an entire paper attached to it).
Personally, I don't think teachers should grade outlines. They're supposed to help you organize your thoughts and make a solid argument. They're not supposed to be shiny and perfect.
I make outlines for all my papers, but since I don't have to turn them in, they are certainly not pristine examples of wonderfulness.
Fun fact: You don't actually have to put that much effort into an outline. You just have to put in as much effort as is useful to you.
I had this thought earlier today as I was looking through my downloads folder and happened across a file entitled "The Flaw in Ragged Dick." It was a paper I wrote for a children's lit class I took once. Since I couldn't actually remember what the flaw in Ragged Dick was, I opened up the folder to take a look.
I found it was a very early version of the paper which was mostly just an outline. It was probably something that I'd started at the library and then emailed to myself to finish later.
But I just had to laugh as I read on, because the amount of effort I put into that outline decreased drastically as it got to the end, and it was kind of goofy. Here:
You can kinda see where I just kinda said, "Yeah, yeah, yeah, I get the picture, whatever, moving on."
See? Outlines. As much effort as you feel like putting into them.
And if you feel like not putting in any effort at all, that's just fine. Your paper, man.