I can appreciate why the Buddha didn't believe in using his position for social reform, like perhaps encouraging the many kings who worshipped him to give up war.
The problem with social reform is it doesn't address the root of the problem. It can result in a superficial change - but the underlying mental conditions that caused the problem remain intact.
For example, take the racial integration movement in America - after a long and hard fought struggle there's a modicum of equality and respect for the African American community, but the engine of hate in American society remains intact and has found new targets - like gays or Muslims or fat people - essentially anyone noticeably different and vulnerable.
This isn't isolated, I am unable to find a single example where social reform changed the underlying psychological condition that caused it. The dirt merely got swept under the carpet to emerge sooner or later in a different place.
Perhaps the Buddha struggled with this too, because he didn't totally stay away from attempting social reform. "Don't butcher your own meat or cause it to be butchered" seems like one of the well meaning attempts, but in the light of over two millennia of evidence it is safe to say, it has largely failed even though there were a few isolated periods where it worked.
There is no room for reform if people don't fundamentally change. Change has to be at the individual level, not at the social level. They have to become deeply aware of their intentions leading to actions, and optimise their existence for freedom from suffering.
Where the Buddha or Buddhists did attempt social reform it has become farcically tragi-comic. Some Asian Buddhists release birds to gain merit, except it produces a thriving trade in trapping birds to sell to Buddhists. Likewise, since slaughter is against Buddhist ethics butchers in Thailand are generally from the Muslim minority. Neither attempt at social reform actually works as intended.
This isn't a purely Buddhist finding. It is a very Indian sentiment. In the Bhagavad Gita, Lord Krishna doesn't ask Arjuna to stop being a warrior or give up fighting, for he knows that his destiny in this life is to be a warrior. However, he teaches him to stop reacting to pain and pleasure with aversion and desire. As far as I know, nothing is ever said of what happened to Arjuna in later life times, but if he did follow the teachings of Krishna, I imagine he became a non-violent person in a few lifetimes.
I was hoping to trigger a reexamination of platforms like right livelihood with this question - because too often I see examples of arms trade or butchery as proscribed activities, but both continue to happen in Buddhist lands.
My personal view is intentions matter. Right livelihood isn't so automatic as not being a butcher or arms dealer. Many people are looking for a table of modern professions with a checkbox of wrongness or rightness next to it. That's never going to happen because it is a doomed exercise. After all, these days a company like Monsanto can even turn selling farm supplies into an unethical profession.