More misinformation. They aren't even close to that expensive unless you are getting the honeymoon suites with butler service or other similarly ultra-premium suites/cabins. Sandals resorts have to be booked well in advance because all the cheap rooms (which are still amazing) get booked first.
I have been to Sandals resorts 5 times now and not once have I paid anywhere near that. The highest I have ever paid was $3300 in peak season for a mid-tier room with a private (for the group of villas) infinity pool at one of their more expensive resorts to get to (Grenada). Every other time has been $2200-2600/pp including airfare in standard/deluxe rooms. They also have resorts in about a half dozen different countries, and Jamaica is the cheapest (below $2000 off season for a normal room).
Most 2-tank dives are $250/USD per day in the Caribbean or Hawaii, so if you're a diver it doesn't take long to claw lots of value back out of Sandals, or make it equitable to a much cheaper resort in which you've paid for some excursions. Things like Snorkel tours and water toys are free, and food is miles ahead of any standard all inclusive resort which for me is a big draw to them. There is also no tipping (staff can lose their jobs if they accept one) so you are saving a few hundred there as well.
The only way you are paying $6500/each at a Sandals is in an ultra premium room.
Just as an example, if I look right now for later in January/February which is part of peak season for Sandals, their most expensive resorts in St. Lucia can be had for $3,500/person including airfare with upgraded rooms. If I go to their most expensive resort which I believe is Antigua, even if I pick a "Seaside Honeymoon Butler suite", I am nowhere near $6,500/pp including airfare.