I have a theory on this. In real life, bullies (for that is all the trolls are) target those they see as weaker than them, knowing that spewing venom at a bigger man will get them punched in the face. Online you cannot tell how big another guy is, and though they are not likely to ever meet in person, the aversion to taking on someone who may be stronger remains, if only subconsciously. Since bullies tend to see women as weaker (the misogyny you mention), the trolls feel safe attacking women online.