There is a lot to be said for being marooned on a tropical island. You don't have to shave every day. You don't have to go to work. You don't have to pay bills, bills, and more bills. You don't have to file your income tax return every year. You can sleep whenever you like. You have nothing to worry about but finding a little food, and if you get marooned on a good island in a good latitude you can find plenty to eat, including coconuts. I think this is what appeals to readers--the fantasy of being totally free and owning your own little domain. The author, Daniel Defoe, made things even easier for Robinson Crusoe by having the hulk of the wrecked ship wash up not far from shore. This enabled Crusoe to supply himself with all kinds of useful things, including tools. He also saved some domesticated animals, and he helped himself to a large quantity of weapons and a huge supply of gunpowder.
The movie Cast Away starring Tom Hanks was obviously a sandwiched-together knockoff of Robinson Crusoe and Enoch Arden. But the island on which the Chuck Noland (Tom Hanks) is marooned is nothing like the tropical paradise of Robinson Crusoe. Chuck Noland has a miserable life for the whole time he is marooned on a tiny, cold, inhospitable island. He even thinks of committing suicide. And he has no tools to work with except for a pair of girls' ice skates that washed ashore in a FedEx package. Then when he finally gets rescued he discovers that his girlfriend has married somebody else (like the hero's wife in Enoch Arden by Alfred, Lord Tennyson). There is something to be said for losing a girlfriend, or a wife, too. Chuck Noland has years of back pay coming, plus retirement pay, plus compensation for being in the FedEx crash. He can have plenty of girls, but he doesn't seem to appreciate his good fortune. The movie is a downer, or actually a double-downer. Everything bad happens to him. It made a lot of money, but I don't think many people would want to see it a second time.
Robinson Crusoe remains popular because the reader can fantasize about getting away from the rat race and going native in a place where the sun shines every day and Mother Nature provides all his needs, as if he were in the Garden of Eden. Naturally Crusoe eventually runs into troubles, because good things never last. But the adventure part of the story also makes it interesting.
Robinson Crusoe was popular when it was published and continues to be popular today for a variety of reasons. I think one major reason it has maintained its popularity is because it is an exciting book to read. It's got sailing, shipwrecks, storms, survival in the face of insurmountable odds, etc. That stuff is exciting to read. In terms of a very surface level comparison, Lone Survivor, The Martian, and Life of Pi are all about a single man's will to live. Just like Robinson Crusoe. People like reading those kinds of stories. They are going to see those kinds of movies, too. Each of those three named books has been (or will be this October) a big Hollywood film. Robinson Crusoe has been adapted to the silver screen multiple times, and even Tom Hanks's "Castaway" bears incredible similarities. Even TV has gotten in on the bandwagon. Bear Grylls has made a career of "surviving" on his own. Don't forget about shows like "Naked and Afraid" and "Survivorman" either. One man's survival is addicting to follow.
But more than just being exciting, Robinson Crusoe dealt with and deals with today themes and issues that people can relate to. There's stuff in there about religion, which always gets people heated for debate (Life of Pi was full of it, too). Other hot button topics that Robinson Crusoe tackles are wealth and social class distinctions. Both of which were important to readers when it was published because of the newly emerging middle class.