It's basically the concept, being able to take someone inside of you or be inside of someone.
The idea and "feel" of holding someone/being held inside of someone is stimulating to the mindset for some people. It can also be derived from the rush of adrenaline it gives some people.
For some, vore is like a concept of "fear" and I use that term in quotes because some get their own joy from the adrenaline of fear, being devoured whole by a monster, making them think their life is going to end, or watching their best friend get eaten alive, seeing them disappear before their very eyes, is a part of the "fear" concept to it.
Then there's also the concept of growth, and this can also be meshed in with belly lovers, watching or feeling or being the one to make someone else's stomach grow outward is also a part of the arousing concept. It merges with the "fear" concept as well because usually some vore lovers like the idea of "bulging" which is where you can see the body of the one who was eaten push outward from their stomach, being able to be seen by the outside world while also being hidden from it. Macrophilia is also a part of the growth concept, Macrophilia, if you don't know, is the idea of growing bigger and larger then cities and becoming massive. "Larger then life" so to speak. The video game "Rampage" or any of the Godzilla movies would be a good reference for that. Eating small people, making yourself feel dominate and power is also what drives the appeal for people.
Then there's the love concept to it. Being able to take and hold your lover inside of you, or being inside of your lover, is also what drives some people. It's a part of the "being protected/protecting" feel. Shielding the one you love most from the world, "hiding them away" and keeping them all to yourself.
Next is the concept of submission. The idea of feeling weak/vulnerable, and submitting your body to those who are more powerful and stronger then you are or ever will be. Making your body a part of their own and "being a part of something much bigger". Lot of vore lovers are usually "prey" because they derive off of this concept.
Then there's Digestion. This concept is also a "love it or don't" for vore lovers. It's a 2 sided thing for them, a lot of people like it, and a lot of people don't. They don't like the "painful" idea, and "death" that it comes with, losing your body etc, but, as for those who do like it, they either, like the concept of death that it comes it, once they are eaten, that's all, they are gone forever, or they chose to keep it entirely just fantasy based where the person is digested, but that's all, his/her body is melted away, but then "reforms" once again in front of the person who ate them or reformed somewhere else, at home, in the park , or wherever else they once where.
The power of imagination
Since it's all entirely fantasy based, reality doesn't and shouldn't be defined to Vore, because it has a big wide variety to it. Some choose to keep it reality based, and some choose not to. Regardless of it all, eating someone else whole is ALWAYS going to be a fantasy based thing because in reality, it's not possible unless it's hard vore, which is another whole subgenre in itself where you eat someone by eating parts of their body in chunks, like cutting them up etc. A lot of vore lovers aren't really much for that.
As for the "Preds", its all the same concepts for them, but just vice versa. Feeling of dominance, feeling powerful, protecting those they love, etc etc
As for being into it in the first place, I, personally blame the cartoons, like this for example:
Growing up seeing others eat each other in a cartoon matter, etc. It's pretty much the same reason why people like inflation, cause thats also a heavy influence in cartoons as well. Particularly Looney Tunes, MGM, Tex Avery, etc. Then there's also stories like Little Red Riding Hood, Wolf and the 7 little pigs, etc.