Why wouldn’t the government merge FATA with the NWFP

Re: Why wouldn’t the government merge FATA with the NWFP

I remember reading somewhere that an outgoing British officer in 1947, advised their slaves to keep the FATA the way it is because the tribals will serve as unpaid defenders of western border for Pakistan. I think this is the main reason Pakistan is not interested in abolishing FCR and integrating FATA into NWFP. Now they are talking about changing some clauses of the FCR but not fully abolishing it.

I can not find the reference to my claim though.