Vegetarianism is hard if you eat meat!

As the son of a devout and zealous vegetarian I've been exposed to the lifestyle for many years. 18 in fact. Up until I was 18 I was a strong follower of Kashrut (kosher law in Judaism) and had little option to eat a large amount of meat. From birth to the age of seven I was a vegetarian so I have a slightly more intimate understanding than I would otherwise have were I never a vegetarian. However, since being 18 I have experimented with various foods of which a large portion is new meats, pork included.
After the last article and discussion on moral justification and necessity of meat in the human diet I debated with myself and decided to try to be a vegetarian again to see if I felt any different or any worse, etc. After four days of strict vegetarianism utilizing the likes of Quorn products and veggie stir fry with little to no fat to cook with, and other BM inducing foods I was forced to cave, whether due to my weak will or dietary needs. My body yearned for that hamburger and as soon as the opportunity arose where meat was one of fewer options I gave in and got the burger and MAN did it taste good!
I couldn't ave possibly predicted how difficult it would be to wean myself off of meat especially as I have been a veggie before. If people don't really need to eat meat why does it seem to be such an intrinsic hard to shake habit?