Is there a practical (UX driven) reason for why login pages often don't have headers/footers when the rest of the site does?

Question

I'm designing a website with a login screen, so I've been looking around at examples on other sites to get a general feel for the UX/UI trends in the area (I'm primarily a dev, not a designer). I've noticed that sites that have headers/footers seem to lose those when you go to the login screen, and the only thing you see is a simple login form, centered (in either 1 or both axes), with a simple company logo.

I'm wondering if this is simply a stylistic choice to keep it simple, or if I'm missing a more nuanced reason for ditching the headers.

Is it bad to have headers/footers on the login page?

Some examples

www.microsoft.ca -> has a header at the top, but the login screen is completely different, and lacking a header/footer

www.google.ca -> the top links are missing when you click on Sign in

www.amazon.ca -> again, the top nav is missing entirely (I sort of get this one, since their header is primarily search based, but this also applies to woot.com, which just has categories in their header).

wwww.github.com -> another one that presents a clean sign in page, although if you try to create a new account, the headers return

A counter example stackoverflow.com, ux.stackexchange.com -> unlike stackexchange.com, stackoverflow and ux.stackexchange.com keep their headers whether you're signing in or registering.

Answer 1

In order to minimize the number of stimuli - at the moment when less information reaches us, we are able to focus on the goal.

Exactly the same with, for example, shopping processes to reduce the page drop rate during the process.

It's correlate with reducing memory load:

• App has a clear structure
• “Recognition over recall”
• Implicit help
• Visual aids

Answer 2

This is a focused task and the key to entering access to the content.

1. Some choose to show some content to pull the user in, but lowering the cognitive load is important to a focused task.

2. Some choose to hide all content because it should not be viewed without privileges.

If you go with the first approach, deciding how far to lower ithe cognitive load will depend on how your users respond.

1. Do they drop off because there is too much noise?
2. Do they come into the site more often because the content teases them in?