Why are most social media web forms on the right hand side of the page now?

Question

I am doing research into social media sites, and one thing I have noticed is that most of the main players in the social media and communication world (Facebook, Twitter, LinkedIn, Microsoft, Google) all have their registration forms/sign-in pages on the right hand side of the page.

What I don't get is that I have been taught that generally, the most important elements on the page should start top left of the page (in Western terms). I know this maybe wouldn't look as good, but was just wondering why forms generally are on the right of the page? Any particular UX reason, or is it just a design convention that was started by a particular site?

Answer 1

When the user comes to the Home page, the user does not expect to see the form top left because it's not the most important thing on the website, from the users perspective. uxmovement has a good article about this.

Answer 2

I think the placement to the right is associated to what is called related navigation. Meaning the social thingies is not part of the content - and not the F shape either. However - when users are going to do something with what they've read - a related task to reading the article - like sharing - then they look to the right since that's where related content usually lives.