In America, most if not all companies have payroll dates. If Google did not stick to a payroll schedule, they would be cutting checks everyday, and that would not be a very efficient way to do payroll. There are other reasons that they all do this, but I believe this is the main reason. I've never work in HR (Human Resources) before, but I have seen how difficult payroll can be on a weekly basis. So, I quite sure daily payroll would be a nightmare.