I think part of it is that we're comparing it to excellent, often "perfect", brisket. If I'm making brisket, I want it to be perfect for my guests. It's not like I make it for a random Tuesday. It's an event unto itself. I disagree with S-Met that it's "****" when done wrong, but would agree that when comparing it to what we all know it's heights can be, missing the mark certainly doesn't end up very exciting.
Brisket is a difficult piece of meat. It's not particularly uniform in size, nor in makeup. The point is significantly more fatty than the flat. The fat cap is often irregular. The area of the flat that overlaps the point will cook at a different rate than the portion that is "bare". The "stall" for each is different. The temp at which they pass the probe test for tenderness is different. Couple that with each one being a little different. One brisket is more or less marbled than the next. One tapers to a thinner flat while another is more thick and uniform throughout. You only have a few at the store to choose from, so it's not like you can pick the exact same size/shape brisket every time. You pick the best one and hope it cooks the same as the last one.
And we regularly want to serve it sliced, such that it perfectly passes the bend test, while being moist without being mushy. To get it into that perfect range, every time, is an art I have not personally yet perfected. While my "mistakes" are certainly edible, and even better than most brisket you'll find at a lot of restaurants, it's hard as hell to make the brisket at the level I want to eat, every time I cook one.
Compare that to a pork butt... It's damn near impossible to screw up a pork butt.