Maybe there is a mooring field there? Wild guess.

Edited to add: 25 fathoms is 50 feet deep. They sell anchor lines that are 250 feet long. So I guess it is possible to anchor out that far. You just have to hope your anchor stays in place and comes out when you need it.But you could scuba down to 50 feet to retrieve your anchor.

A fathom is 6 feet so 25 fathoms is 150 feet. There are sand bars here and there, maybe it's shallower? It's not that common for a boat to want to hang around or anchor in an unsheltered place like that especially if there's a harbor/marina nearby.

An anchor line (chain plus attached line, usually flexible nylon) needs to be many multiples of the depth of the water when there's wave or swell action. I don't remember the exact ratio but I want to say at least 5 X and it could be more. For 25 fathoms of water, that's more than most small boat would have on board.

I learned how to sail as a kid during summertimes. I owned a boat with a partner into my early 30s and had friends with boats. It's a lot of fun. I envy people living in areas where the variety of the waterways (including a lot of islands) is more extensive that what I normally experienced in SoCal and SF Bay. I'm thinking like New England and Chesapeake Bay as examples. We never did a bare-boat charter in the Caribbean but often spoke about doing so. Too late now.

Maybe a vacation spot for them.

From what I read, you need a 3-to-1 ratio of line-to-depth for deep water anchoring. So in 150 feet of water, you would need 450 feet of rode and chain which seems like more than most boats of that size would have on board. That's why I wondered how they were staying on location. No mooring balls in that area.

My bad math. Disregard.

Watch Below Deck Mediterranean! It shows them dropping anchor and pulling it back into the pocket. The anchor is on a very heavy chain that is reeled in and out and it is on a reel in the belly of the boat. The captain tells the crew how many shackles to let out depending on her depth reading. The anchor is very large and heavy. This is a huge yacht.

Are you sure the NOAA chart is in fathoms? Our charts are all in feet, so 25 feet is nothing.

On our boat we carry 100' of chain attached to I think 300' of rope. The 'scope" that Elmer talks about can vary depending on the conditions. In calm water, 3:1 is good. In rougher conditions it might be as high as 7:1.

A marina neighbor of ours once told of someone asking about his trip to Bermuda. "What about at night? Where do you stop?" "Uh, we don't. We don't carry 6000' of anchor line!!"😂

The ocean floor isn’t flat though, depending on where you live, it could be that they are in a location that has hills below the water that make it less deep for anchoring (and possibly great for fishing maybe?). If they knew about that, the spot would be easy to find using a GPS.