First...
An answer to your question, why doesn't he step down for the sake of his people? because it wouldn't make much of a differance, if he steps down, the Military and population have to fight the agressors alone but without an organised body.
Second...
Don't play dumb as if you don't know both sides of the story already, do I have to repeat what others have repeated before me so that you might know? do I have to do a memory check for the readers of this thread? I hope not.
Anyway if you go do a few quick searches on youtube, you can easily find massive Pro Assad protests in capital of Syria, and other places. Like this one, /watch?v=eoaNPefs1sA - youtube.
If the government was killing its own citizens, the country wouldn't be protesting in favour of the government in the 100,000's and millions.
MashAllah, This is a very good point.
Heres that video.