So I have no real background in history (I guess that’s why I’m here). What little I "know" is from here and there, and its been ages since I even remember coming across that stuff. So I just want to apologise in advance if I'm just talking out of my ass. Feel free to just redirect me to a basic wiki/post on Sulla or something.
I know about Sulla and his proscriptions, his failed reforms, the unpredictable terror he was known for inspiring (brings to mind the French Revolution’s Terror), his strengthening of a small subset of the senatorial class, his hypocrisy, etc. He seems to have earned his infamy.
So, recently I was talking to a friend who grew up in the USA. We started talking about the ideals that the USA was founded on and the role of the president as it expanded. We eventually came to the topic of George Washington and the comparisons between him and Cincinnatus. From what I can tell, the Cincinnatus that people seem to know of and is used in this comparison is largely the farmer-dictator who gave up ultimate power in favour of The Republic. But I was wondering if that's what made him so famous, what about Sulla?
So based on my limited exposure to Roman history, I never considered Cincinnatus all too great. He was just another dictator in a line of dictators which had existed before him and would continue for some time. Admittedly, he did give up his dictatorships before his terms were up, when the causa ceased to be relevant. Each dictator, to the best of my memory, obeyed the causa and/or term limits set by the senate. They would rise to the occasion, and then retire to regular political life or to their home in the country. The law and the very notion of “The Republic” still seemed to have some weight to it. The idea seemed to still be alive and respected. Which is to say, the culture was such that it was easy for Cincinnatus to follow the path his predecessors had already tread. But by the time of Sulla it was no longer the same Republic or the same culture, bribery and populism seem far more explicit and the Senate now found it's historical and constitutional power threatened by the mobs, etc. etc. even Sulla's most articulate enemy, Cicero found much to say about the state of the Republic (IIRC). Furthermore, the office of dictator had been empty for, IIRC, like 4 generations. With this limited understanding of Roman history, it seems rather astounding to me that Sulla, isn’t to some degree, praised/known for putting aside his dictatorial powers, which were indefinite in both scope and duration, and retiring to his farm (see idyllic farmer-dictator concept mentioned in previous paragraph). Admittedly, it seems he still held real power even after he stopped being the dictator.
But yeah, why isn’t Sulla remembered for surrendering his power when he could have easily held onto power even longer? Shouldn't this be something that's equally famous, as Cincinnatus giving up his dictatorship when the causa was satisfied?
You've asked a question that is pretty impossible to answer. You are right that Sulla set aside his dictatorial power and essentially "retired," but not before he had corrected what he thought were Rome's biggest problems in an iron-fisted campaign of bloody reprisals. In order to attain the dictatorship, he twice marched on Rome with a Roman army, entered the capital by force, and conducted senate business while the curia was surrounded by his troops. History has not forgotten what a brutal and merciless person he was.
On the other hand, he was an incredibly successful Roman aristocrat according to every metric. He was a member of the gens Cornelia, one of the most ancient and respected families in Rome, blue-blooded patrician. He rose to prominence on the cursus honorum more or less the "proper" way, not skipping steps (like Pompey, or Octavian). He was an insanely competent general in the field and during the Social War was awarded the corona graminea -- that Grass Crown, one of Rome's highest distinctions. The number of Romans who got it legitimately are in the single digits, and that's over hundreds of years. His troops hailed him as imperator several times, also a rare honor at the time (later it would become so mundane as to mean nothing).
Washington probably gets the comparison to Cincinnatus instead of Sulla because, well, Washington didn't undertake a campaign to murder all his rivals. Sulla is more of a "real" person, in a more historical epoch, and tends to be remembered for the bad instead of the good. Cincinnatus is earlier, more idealized, and archetypal.
I'll also go wildly speculative here and suggest that Cincinnatus might have been better known to the founding fathers than Sulla just in general. Livy was a "core text" of a good classical education, especially the first book, while Appian and Plutarch were perhaps more ancillary, besides being written in Greek instead of Latin.
The biggest difference is Cincinnatus was given power and gave it up whereas Sulla took power from the Senate similar to Julius Caesar. Cincinnatus was considered an ideal dictator to the Romans because he was called upon in crisis, fixed the crisis, then gave up power. Sulla may have given up power but in Roman society but that was expected of dictators however they shouldn't have taken power and they need to make things better when they take power.