No-one knows how many people have a totally different private opinion from what they say openly. If you are Iranian, for instance, and an atheist, you would be insane to tell anyone. Better to go through the motions and just pretend.
As an atheist I find normal Christianity very safe and unthreatening. I don't like evangelical Christianity - it has caused a rift in my family, between my late nephew's widow, and my nephew's atheist Dad, my brother. She has simply rejected her in-laws 'cos they are not co-believers. I think she got involved in the church in York, when my nephew was dying.
Islam is far too 'in-your-face' for my liking. Why wear Islamic dress in a non-Islamic country. All you do is set yourself apart. Praying 5 times a day?? What a nuisance that must be. But I would never be rude to anyone for their religious practices - I just don't understand them. I do believe that even in Western countries there will be many atheists from Muslim families who keep quiet about their lack of belief., for the sake of peace
I have the same attitude to Judaism as to Christianity - it is usually low key and very unthreatening, especially nowadays with so very much intermarriage. Mind you, atheist Jews are not usually reticent about their lack of belief. My last boss was one, and we used to laugh about 'Jewish atheism, and 'christian' atheism.
But - my point is that stats on belief v unbelief are skewed - people have a lot of reasons to fib.