Because you have become addicted to socialization in the form of the internet and television. These require less of you emotionally. No need for make-up or dressing up or going somewhere when you can get the social intereaction you need right here. If you don't like what someone says you can instantly be at aother website with the click of a mouse. sure it might not be as fulfilling at the start but over time you will replace your "going out" with "staying in". How do i know your addicted? "Why can't i leave my house" is a classic symtom of interent addiction.
So don't you have to leave the house to work and pay for the roof over your head?
you alienated from the society. be more courageous and go to a store. make a change every day and soon you'll be free from your own personal house arrest. and yes, make a project of it. be proud of every executed step you accomplish. you'll get there, you'll see
Start small. Go to the corner store and get a paper. Tomorrow go out a little longer. As for why you don't feel like going out, I feel ya in this cold early dark season.
Don't bother, there's nothing out there worthwhile. I like it at home.