They're "bulkers" because people are still taking advice from the 80's and 90's. Sure, some compounds have very specific purposes like winstrol, which draws water from the subcutaneous layer and other tissues (precontest), but it's all about diet.
Dbol and deca are "wet" because they aromatize, and back in the day AI use wasn't prevalent. This led to 20lbs of water gain, that folks thought was lean mass. While I personally wouldn't want to cut on dbol as it's very anabolic, and can give ridiculous pumps - it is feasible.
I'm on deca year-round, so it finds its way into every facet of composition changes that I undertake.
My .02c