We have seen the recent success of Duck Dynasty make that case as well as long running shows like American Chopper, families are unpredictable, families are crazy...and families sell.
There is the obvious answer in that they are easy for any audience to relate to because we all have families but there has to more. What draws an audience to this kind of dynamic above all?
Have you ever heard of a "functional family"? Not really. All family units no matter what the make-up are a little bit dysfunctional. Why? Because families are not made up of your choice- they are assigned by some higher power and you have no say in the outcome. You get what you get. They can be complied of a bunch of people you love but don't even like. Lets face, that does make for great TV.
TV audiences do relate to the inner workings of families and the added layer of being in business together really adds more drama, more tension- it raises the stakes.
We aren't just comparing ourselves to them to make our family and life seem less dysfunctional, sometimes were are rooting for them. We want them to defy the odds, overcome the gene pool lottery they were handed and come out on top.