Because it's really not. A confederate flag is a symbol. True, there is no reason on earth it should be flying above a government building. But a glad is a simple thing that could (and should) be taken down. It's the equivalent of putting a band-aid on a toddler's scratch. It makes the situation seem better, but it does not in itself affect change.
What we need to do it to have honest, and real, and painful discussions about race, and the racial divide, in this country. We have to stop hate groups from profiting from their venom, and inciting others to join them. We have to fight the demon of poverty in this, the richest country in the world, which heightens racial issues. We have to teach people that violence is never the answer, or even an option. We have to demand responsible gun ownership in this country, so that no one ever gives an obviously disturbed young man a gun for his 21st birthday. We need to strengthen — no, we need to completely reinvent — mental health advocacy and services.
The confederate flag needs to come down for sure, and should have a long time ago. But it's not even a first step in this, and we're fooling ourselves if we act like it is, or if we don't do the real work because we got distracted by a symbol.