Who says it is common practice to eat 3000-4000, I have never heard of that. My advice is that you add 500 kcal to your BMR. When your bodyweight has stablilized you add another 500.

i guess i just don't understand bulking

Determining BMR is not as simple as pulling a number out of a book. It's very individual to bodytype, lifestyle, and type of diet consumed as is how many additional calories you should take in while bulking. The best approach, in my opinion, is to make regular use of an accurate scale and some bodyfat calipers gradually adjusting calorie intake up or down accordingly.

gaining weight be it muscle or fat is all in the surplus of calories

most people tend to eat 3000 to 4000 calories because it's a good surplus amount as on average most people maintain on calories between 2000-3000