BCAA's are great, but there are other essential amino acids (EAA) that your body needs as well.
They are called essential because your body cannot produce them on its own and must get them through dietary means. Thus, it is wise to consume good quality protein such as whey, eggs, beef, chicken, etc.
Furthermore, there is the issue of satiety, BCAA's won't do anything to make you feel like you've actually eaten something. Whether bulking or cutting, most people enjoy feeling satisfied after a meal (and that is all the more important when cutting).
Cost is an issue as well. Granted, in terms of BCAA's, buying a BCAA powder will be "cheap" in the per gram sense. But when weighted across multiple categories; such as EAA content, Calorie content, Satiety, then it becomes an expensive way to get your nutrients.
BCAA's are a great supplement and I use them to ensure I am getting quick amino acids peri-workout to help support protein synthesis and prevent breakdown, but during the rest of my day I eat whole foods.
A couple of other strategies to use BCAA's:
1. See Layne Norton's article for between meal spiking of protein synthesis (I don't do this when bulking, but I have spiked between meals when cutting to help preserve mass)
2. If you are eating a crap meal and the leucine content is low, add a teaspoon of BCAA to help get that meal up to the leucine threshold (typically around 3.2 grams) to help that meal stimulate protein sythesis. (I actually do this when my wife makes spaghetti and meatballs, tastes great, but I know I am not getting much protein or leucine either)