No, they are not very popular today. With the development of digital technology, most people prefer to listen to scary stories on podcasts or streaming platforms. These are more convenient and accessible.
In my opinion, they are worth collecting. The scarcity of these tapes in good condition is increasing as time passes. Also, they can be a great conversation starter. You can share your collection with friends who are into horror and talk about the different stories on the tapes. It's a way to preserve a part of horror history that might otherwise be forgotten.
You might find them in second - hand stores. Some old - fashioned thrift stores often have a section for cassette tapes, and you could potentially dig out some with scary stories there.
In a particular FNAF story, a group of kids dared each other to spend the night in the abandoned pizzeria. As the night fell, strange noises started. The animatronics that were left there in a dilapidated state began to activate one by one. The kids realized they were in real danger as the animatronics moved towards them with an unnatural speed. They tried to find a way out but the place was like a maze, and they were constantly being chased by the terrifying animatronics.
I'm not aware of any official connection between GTA 5 and FNAF in terms of scary stories. GTA 5 has its own dark and gritty stories, and FNAF has its own spooky lore, but they are from different franchises and not typically combined in that way.
The fact that it's based on a true story, if it is indeed so, makes it scarier because it feels more real. It makes you think that such horrible things could actually happen in the real world.
The back story of FNAF 4 is scary mainly because of the nightmares. The main character is a child who is haunted by these terrifying animatronics in his dreams. These nightmares seem to be related to the dark secrets of Freddy Fazbear's Pizza. The animatronics look more distorted and menacing in this installment, which adds to the horror.