Why does the US Air Force need 2 organizations to do what the Army and Navy do with one?

Seriously?

When was the last time that you were on an Army post?  You can't tell me you haven't noticed the hoards of DA police doing the same job as MPs on pretty much every base.  Some posts don't even have military MPs.

The Navy also has civilian LE.  

It is literally the exact same thing.

Also, DAF civilian cops and SF don't do the same job.  Air Base Defense in not in the job description of 0083s or 0085s.  

Also, they aren't 'organizations.'  DAF Police refers to civil service 0083 and 0085 personnel. Security Forces refers to uniformed personnel holding the AFSCs 3P0X1 and 31PX.  The term 'security forces' can also be inclusive of DAF cops.  At the base level, they are both in a security forces squadron.

"Department of Air Force Police" is the title for the civil service police or civilian contract police hired by the AF to work within the overall Security Force function. It's only one function with a number of members with different source legal statuses.

it the same squadron, just different flights inside the squadron

The link below will answer your question.