Abusive relationships and the consequences

So In my social work text book today I read about how men who abuse women, and end up killing them typically only face 2-4 years in prison. However , a women who kills and abusive spouse out of self defense is typically given 10-15 years and are charged with premeditated murder , because they have had plenty of time to remove themselves from the situation and “expected” for this to have to happen. What are our thoughts on this? Is this sexism in the court room, or is this a misunderstanding by the judicial system being uneducated?