Maybe some thieves stole those parts off of it in the middle of the night while it was moored at the Marina, then towed it out and pulled the plug?
Nah, I say insurance. Some years ago, at a FL business roundtable meeting, I spoke with a older fellow who had been the national president of the Chris-Craft owner's association. When I mentioned I was from the Chicago area, with a family place near Lake Geneva, WI he spun a tale of fraud. Seems that in the upcoming era of fiberglass boats, wooden boat owners tired of heavy and expensive maintenance figured out a way to switch to lighter, faster and near zero (hull) maintenance 'glass boats.
How, one asks? They pushed their Chris Craft and Gar Wood boats into the lake, punched a hole in the bottom and then collected insurance money!
His staff at the CC association was cataloging at some expense old insurance records of "lost" boats in northern salt-free lakes where old wooden speedboats were common. They had identified at least 100 sunken boats, 2-3 in Lake Geneva, and actually raised maybe 20+ at that time (maybe 1989?) with the idea of restoring them for sale. Intrigued, I asked about condition and other than broken windshields from dropped anchors and rusty engines, the hulls and stainless steel brightwork were in great shape. I'll bet some are still searching waters all over the Midwest and maybe elsewhere for nautical barn finds!