I had a claim on my boat after it burned in the drive way and on the trailer. I had two surveyors examine the boat,(one hired by me) both agreed it was a total loss. They told me that the only thing good on the boat were the Bravo outdrives. Why would they be worried about a missing starter, water temp sensor, oil pressure sensor, and spark plugs????? If these are "junk" or have "zero value" what is the big deal???

Probably because you are insuring a running boat not a hull and they will want to knock off big money if the motors are not in working order before the burn. Just a guess

Sure they weren't implying the fire was related to the boat not being in running order?

Im not sure what they are implying. However the boat was in perfect running order before the fire.
I will never understand how an Insurance company can demand you the customer to pay your premiums on time, but drag their feet when its time to pay up on a legitimate claim.