I'm not sure if Assad is even that unwilling to step down. Based on his history it's obvious that he never wanted the job. He inherited it, accidentally.
The problem with stepping down from power in Syria, is that he would likely be Gaddafi'd by the next government, and his family and friends would be purged alongside with him. So there has never been a choice to peacefully transition power to someone else.
Part of that is his own fault (and the fault of his ancestors), but part of that is simply the law of the land. A cornered man, without choices, is going to fight back like an animal. A lot of the people who fight for Assad, know fully well that they don't have a future without Assad. The next government would punish anyone associated with the old one, and nothing would change. The previous government would become the new oppressed, anti-government.
If the West truly wants to get rid of these dictators, then they have to be more rational and capable of seeing things from their perspective as well. Can we really expect these people to give up their positions, after seeing how Gaddafi and Saddam went out? Humiliated, degraded, whole families wiped out. No matter how brutal they were, all it does, is encourage the next one to be even more brutal, in order to stay in charge.