Why Do Leftists Ignore Islam?
I suspect that's due to the common belief on the Left that history runs in only one direction. They figure Islam was already defeated (it was down for most of the past few centuries) and now it's Christianity's turn.
When leftists see evidence of Islamofascists in action they think of them as part of national or racial liberation movements. That might be why they attribute opposition to the Islamofascists to race prejudice.