"Use of the arm" in the Wolves v Leicester game, in many people's opinion Wolves had a perfectly good goal ruled out.

The pundits on MOTD2 all defending it because it's now "the law".
Phil Neville in particular saying that everyone knows the rule so get on with it.
Okay yes it is the law but how the feck did it become the law?
Also, this law is interpreted differently in the EFL.

What the hell is happening to the beautiful game and how are the rules being allowed to differ in different leagues?