It's true, all you'll normally see in atheist communities are edgy kids bitching about how grandma said 'God bless you' one night, or again, complaining about their dad asking them to go to church or celebrate Easter. The older, more articulate ones seldom ever criticize Islam, if they do, they only criticize the misogynistic and homophobic parts of it, not the other savagery. And they never criticize Judaism.
My theory is they criticize the easiest possible target. Most of them are leftists so they don't want to step on any toes in their circle by bitching about Islam and being called Islamophobic or racist. Likewise, criticizing Judaism will typically have ADL shills bitching about you. Islam also carries the possible penalty of fucking death for being critical of it, after all, an office full of people got massacred for drawing a cartoon of Muhammad. Criticizing Christians, on the other hand, mostly results in the family looking around awkwardly at Thanksgiving dinner, maybe grandma gives you a dirty look every now and then, and old southern ladies will say 'well bless your heart' a lot. Christians aren't going to cut off your head because you drew a blasphemous picture of Jesus.