It's most likely because you can't see the evidence of God. There's nothing tangible which you can refer to. Anyone can make up books and words and say it's from God. Anyone can claim to be a prophet. When some people say that everything is created by God it just doesn't make sense to an atheist.
I read your introduction. I too read the Maariful commentary. I've also read Ibn Kathir, I can't say I was too impressed or enlightened. There are some useful, interesting parts in terms of historical context and things you could relate to but I think it could be improved.
Well, if there's nothing tangible there, and no evidence as to the existence of god, why do people believe? Even more interestingly, why would people center their lives with such certainty and zeal around such a belief, which would at very best have tenuous support, and none that's particularly rational?
Without evidence for supernatural claims, they can be dismissed outright. The problem with organized religion, and especially Islam as it is commonly practiced, is that it does not leave room for such a dismissal and diversity of thought from a young age. Everything about Islam, from rituals to historical narrative is tailored to promote conformity. And beyond that, there is the oftentimes denied and unspoken reality of retribution and shame which accompanies apostasy and silences the dissident via fear.
Hence, this forum to me makes perfect sense, and I'm interested to know what exactly "blew you away" about it? In light of the lack of evidence of any Islamic supernatural claims, and Islam's inability to accommodate dissension, such forums would be the natural product, no?