1. An abundance of Anti-Islamic Propaganda (turn on any news station and try to not find a reference to Muslims)
2. An abundance of Atheist Propaganda (all over social media platforms, doesn't matter if you are watching a video of cat's playing)
3. An unfortunate amount of Sheikh's who would rather spend time talking about past events or stupid issues labeling EVERYTHING haram. (this hair cut is haram and will land you in hell, pokemon is haram etc.)
4. Lack of Muslim Philosophers and finance to scientific fields in the Gulf.
5. Muslims lacking knowledge in their own religion. (Not that they do not memorize the Qur'an, but they lack the knowledge in a lot of areas.
6. They often get persuaded by worldy gains (Parties, clubs and drinking) so abandoning religion will obviously make them feel less guilty and they do not like the notion of being judged when all they want to do is take a moment to "relax". This reason however, i have seen almost all of them eventually return to Islam even stronger. Then again this is subjective.
The most powerful problem has to be the internet and sites such as wikiislam, answering islam and answeringmuslims and whatever.
We have these Christian fools trying to refute our religion while promoting their own which is hilarious at first, but not as funny when naive muslims fall prey to their traps. In addition to Osama's site which absolutely rips through Christian creationism, check out this other site found called ( science-of-the-bible.blogspot.com ) to get another view-point of such a morally, historically and logically bankrupt religion. You obviously must have heard of other brothers such as Sami Z. and many others who have sealed the coffin on Christianity.
I almost forgot, the majority of Muslim leaders at our time aren't that smart. They'd rather spend money on unnecessary infrastructure and useless empty buildings than defend Islam online with all their money. For example, here in Kuwait. Sites like Answeringislam or Harun Yahya are blocked on several ISP's. But the real question is... why don't they bring Muslim scholars together to respond and refute such allegations INSTEAD OF just blocking them and declaring it to be HARAM? That's their only defense these days, sadly.