Why do many companies hide their navigation during the Sign-In and/or Sign-Up flow?

Question

I have been tasked with designing a sign in flow, but I have noticed that many companies hide their site navigation during their sign in/sign on flows. I've seen quite a few articles on designing these flows, but none of them mention site navigation (take a look at Login Form..., 18 UX Design Tips..., UX Login..., 10 tips..., and Designing a...) You don't have to click on any of those because they all have the same basic information, none of which includes "hide your site navigation"

The examples that I have looked at include:

• Hubspot
• Starbucks
• Amazon
• Ebay
• Stripe
• Mailgun

I have a lot of guesses, so let's steer away from speculation if possible, I'm looking for behavioral reasoning or data/numbers on conversion rates.

Thanks!
-Drew

Edit: So in order to get a user to complete a task, they remove navigation because it's perceived as 'noise'? Is this a practice that is done with tasks? Complete any task on this site. Send a message, reply to a comment, change your avatar, ask a question. Does navigation disappear? No.

Good UX practices make things easier for the user, dark UX practices make things more difficult for the user in order to make a sale or convert. Preventing the user from freely moving about the site in order to get them to sign up is dark UX. I would not feel like a responsible UX designer if I told the developers to remove all navigation from a sign-up path if the only reason was to get them to do it.
However if users actually find it helpful, I'm sorry, but I need proof and not guesses. (qualitative: 79% of users say "I HATE navbars when I'm signing up" or quantitative: "sign ups went up 12% when we implemented XYZ")

Answer 1

In short, it's because you usually sign in with a different website that doesn't have those elements.

Many logins are handled using OpenID Connect/OAuth 2.0. It works like this: you trigger an action that requires signing in (eg. you click the log on button, you try to navigate to a protected page), the website you're using redirects you to their authentication service which serves you a login page, you fill in your credentials the the original site and authentication service interact to sign you in and establish a session, in the end you are redirected back to the original website.

So they're not hiding those elements, they actually don't exist on the authentication service's login page. Login pages are usually minimal (usually a form with two inputs) and have very little third-party code which reduces security risks. The security of these pages is very important because they capture usernames/emails and passwords.

Another benefit of using an authentication service is that it enables single sign-on (SSO) across a company's many different services (eg. Google, Microsoft). You can sign into Gmail and YouTube will be logged in too.

Answer 2

I think the main purpose of sign up page is to make sign up, adding navigation can disturb user from completing that. that way I think most many companies hide their navigation.

Answer 3

The purpose of a sign in journey is to get the user to sign up. This is the only goal/requirement of the journey as a whole.

Any distractions risk the conversion (in this instance a sign up of a user). If a user is distracted by something in the navigation (etc) or any other visual elements the conversion is lost.

It is way more valuable (in the sign up journey)to get the user signed up than to have them distracted by something they may or may not interact with/buy. This way it opens up more benefits and opportunities for the business like; marketing, notifications, data and a slightly easier buying process.