What could be the reason why my feet are always cold?

Cold feet: Circulatory problems are the most common culprit for cold feet. Blood must travel a long way to get from the heart to your feet, and there could be many factors causing it arrive more slowly (or with less volume). If you are a smoker, this is one of the largest factors. It could also be caused from the way you are sitting if it is for a prolonged period of time. Or just wear thicker socks.

Vascular: If this is a signficant severe problem for you, then i would see a physician for evaluation of possible vascular (blood flow) insufficiency. It is also possible that this is completely normal for you, and there is no underlying pathology.