Those multimillion dollar mansions sitting there empty may well not be worth what you imagine. It could cost as much as a new house does to fix them.
Cold hard fact of life is that a house at the shore has an ongoing cost base that far exceeds the mortgage.
I spent 15 years living literally under that salt spray 70 feet from the water in San Diego, at night you could see the spray falling on your cars and home (in my case a 110 year old shack).
For the none rich beach dwellers, alley picking became normal because of the fast turnover of people moving in and out. One soon learned that everything (brass lamps, toaster ovens, BBQs, metal fans, tools, metal shelves), looks used, rusted and old after 2 months anyway, and that you will not be taking most of what you own with you, when you move away from the beach, so we just pass it on by putting it in the alleys.
When I have seen “Two and a Half Men” I can’t help but think of what it takes to maintain that place, that patio door would look like heck, the piano would need lots of attention, the salt and moisture destroys electronics etc.