Couldn't I just eat Low carb, high protein/fat diet everyday?
You could. That's a very reasonable approach. However, you should plan to fail at that once in a while. Set a 90% clean goal and if you fall short once in a while, you have room for improvement. It's like a failsafe against backsliding.
The reason "The Anabolic Diet" uses the weekend carb spike, is to get an anabolic boost from insulin. It's for a short period so it doesn't encourage fat retention. I'm not sure it works or if it just gives you a pump for Monday's workout. I think it's more of a psychological thing.