Why are websites center aligned instead of stretched to fit?

So, in a nutshell, web content is best not to be stretched across the screen and keeping it centred reduces head movement, even moreso then left aligning your content would.

1. Should websites be centered?
2. Why is alignment on a website important?

Should websites be centered?

Centering the content puts it in the place that will most probably be in front of the user's eyes. Ancillary text not intended to be read in detail during lengthy periods, like navigation and the like, can be set off-center.

Why is alignment on a website important?

In general, your website elements need to align for full functionality. If your website user thinks they are pressing a button or link, but this is not properly aligned, they may simply think your website is broken. Not only will they leave, but they will also be less likely to feel positively about your company.