Milosevic was hardly a small player. He had as much influence on the Serbs (until cutting off support in 94) as Tudjman did on the HVO.
While it was hypocritical for the West to slap sanctions on Serbia and not Croatia, the HVO did nothing as dramatic as the sieges of Sarajevo, Bihac, Gorazde etc. - although the shelling of Mostar, and the killings in Ahmici and Stupni Do did great damage to Croatia's image. Lucky for them, the Serbs stole the spotlight, leading the US to back them as a means of levelling the playing field.
When it comes to understanding the Serbs, it was a little hard for the world be to sympathetic when they had the Muslims confined to six cities, out-gunned their enemies in tanks and heavy guns and had a leader who regularly said things like:
"Muslims faked the whole thing, using actors and old, smuggled corpses."
That's Karadzic quoted in TIME magazine after the Feb 6, 1994 mortar attack on Sarajevo that killed 68.
I remember at the time wondering "Is this guy for real?"
Granted, the Muslims waged an aggressive, manipulative PR war designed to get the West to jump in on their side, but they didn't have to try very hard to make the Serbs look like the bad guys. They played the part wonderfully on their own.