Why most people find it scary to go out in the dark

I don't like going out at night by myself, even to cross a 6m bit of drive to get to the garage. The other day, my friend and I went for a run at 8pm, in the dark. I went along because I wanted to get some exercise and I hadn't been outside much that day and wanted some fresh air. While in a way I enjoyed the run -cold air, loud music, feeling that I do something with my life- I also didn't enjoy it in that I had to run to my friends house to pick her up on the route. It was cold, dark, not cosy, shadows everywhere, flickering streetlamps- all the sort of things that would be included in a horror movie where a gang jumps out and follows you. I think, personally, that the fear of being in the dark outside comes from our imagination and what we watch in horror movies because a cold, dark, shadowy place is pretty much where 'it all' happens. Because I have ferrets and they live in the garage-don't worry, ferret lovers, there are no poisonous fumes..etc- I go out in the evening to get them to have a run around in my sunroom. Its only just bearable, but only because of the light on the wall of the house that comes on when there is movement. The bit I hate the most is opening the garage door into the dark, gloomy space withing and feeling as if someone is there.... but of course no one is- apart from the ferrets, but they don't count. Its all just my imagination playing tricks on me, which is exactly the same when anyone feels that fear when outside alone in the dark.
Normally, when going for a run by myself, I don't. I can't leave the warm, cosy, safety of the house to go outside. With the fire burning, the millions of pairs of socks, the biccys on the table and the warm cup of hot chocolate, I cannot even get off the sofa. It just doesn't happen. I guess I've sort of made the outside at night the opposite to the warm safety of the house, therefore thinking it bad and not nice.
Another reason I have are all the reports of girls getting kidnapped and killed or the 'yobs'who hang around with knives ..etc. I wouldn't want to be in the same road as them on a dark, cold night with no one around......