Macros are designed to allow a player to combine commands and modifiers (targeting, non-GCD abilities) with regular abilities in a quick and efficient manner. Macros can't make decisions for you. There is no macro that will automatically switch between Mutilate and Dispatch for you on the fly. There is no macro that will use Revealing Strike when it fades and Sinister Strike otherwise. Macros aren't intelligent – they have to be told what to do.
Pure classes tend to have fewer abilities than hybrids, and after the merging of spells like Envenom and Eviscerate, our action bars are sparse. The average raiding rogue might only need a dozen or so abilities per encounter, and that's including defensive cooldowns. A typical assassination rotation consists of Mutilate or Dispatch, Rupture and Envenom, and a few Feints or Cloaks per fight. Rogue macros tend to focus less on day-to-day rotation assistance and more on strategic abilities and cooldowns.