Necks are different usually, I think. The whiskers grow weird, sometimes really weird.
So the best answer is that it's just the way it is for you. See what others say as far as preventing ingrown hairs. As far as rash and irritation, map your beard so you know the direction of the grain, maybe avoid ATG, and back off on the pressure.
1). Neck skin is generally more sensitive.
2). It is easier to make a flat surface on the cheeks, so it's easier to keep a good razor angle.
3). It is easier to see the direction of beard growth on the cheeks, so you can go with the grain on the first pass.
4). Most people hydrate the cheek area better prior to the shave.
5). The hairs on the neck tend to grow out at a shallower angle, leaving them more prone to irritation and ingrowns.
There are probably other reasons, but those are a few just off the top of my head.