Extended Sevice Plan won't cover microwave oven??

I filed a GS extended warranty claim, one of the items was our Dometic Convection oven. Dometic and the RV service department agree it is not repairable. Good Sam advised me a new Dometic/Convection oven is 970.00. They would pay only $450.00?? My deductible is $250.00. I was told they would not replace it. I called GS ESP and asked if could just go to Lowes and get a new "other brand unit" which would be GE or Sharp etc. Exact same size and I would replace it myself( approx 500.00). They said no. I don't get it GS would have to pay less if I went that route only around 250.00??? It should not be this hard to replace a microwave? Any help or a review would be appreciated.