Why only three computers at a time.

I have four computers two desktops and two laptops I don't want to pay 69.99 for three computers when I only need it for one computer. 

 

The other thing I was wondering about is why Norton Internet Security isn't like other programs where they let you install it on your desktop then your laptop without having to get a new license. Since you only use one computer at a time either your desktop or your laptop. I don't use both at the same time.  The same for my wife she either uses her desktop or her laptop but not both at the same time. There are software companies out there that recognize this and allow you to load their program on your desktop and your laptop with only one license purchase.