Google just recently switched from single view to multi-view so obviously people over there feel there are pros to multi-view.

 - You can verify that the account exists even before a password is entered.
 - You can press enter to go to the next field instead of tab which is nice because many users often press enter without thinking since that is what you need to press after filling out the last field.

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Although those are big pros to consider, one step does appear as simpler to users, and users like simple.

 - When users see a form with let's say 5 steps, they will automatically calculate that the form will take 5 times as long to fill out as a form with only one step. They have no way of knowing that each step is only one short field. Here you only have 2 steps, yet the brain still calculates it as twice the amount of time.
 - Multi-view sign in will seem more complicated to a user since it is an entire extra step.
 - By showing everything on one screen, users right away see everything they will need to fill out. Users like to be in the know :)

 - It is easier for users to correct previous field when they can just click on an above field, instead of needing to go back a whole page.
 - Many users will be using touch devices. On these devices, many users prefer just tapping on the next field instead of using tab or enter.