Illustrator Pixel export

You're not doing anything wrong at all. It all depends on where your pixels fall.

Without Anti-aliasing, normally, any pixel is either ON or OFF depending if the average value in that pixel is above or below a 50% threshold (left). Anti-aliasing helps this by rendering the actual average value (sometimes looking at pixels around it). On curves/angles this is extremely helpful, but on straight lines, it will only show if the edge of an object falls partway between pixels. In your example, the vertical edge falls perfectly into the edges of the pixels, hence, no anti-aliasing is needed. However in my example, if the edge falls between pixels (as it does at the top left) it will anti-alias accordingly. Anti-aliasing on vertical/horizontals like this is less desireable in the end, so the algorithm in Art-optimized tends to create a bit sharper edge than Type-optimized (which is really only useful for improving typography at smaller size but makes non-type objects a bit soft)

Nothing is wrong. This is because your images are made of pixels. The line is antialiased, but when you zoom out antialiasing makes edges smoother. Just stop zooming in so much, you won't like what you see.

in the future, to find the best place to post your message, use the list here, https://community.adobe.com/

p.s. i don't think the adobe website, and forums in particular, are easy to navigate, so don't spend a lot of time searching that forum list. do your best and we'll move the post if it helps you get responses.

<moved from using the community>

The image consists of pixels like a piece of math paper. Each square can only have one color. The steps are the only way to draw curves at all. 

Do you really need to export pixels?