Maybe you don't hang around Muslims enough?
You have to understand the context in which these people live their lives and the way they're raised. They grow up being indoctrinated that god is watching them all the time and any dissent with the word of god is considered treason and will be punished for eternity. That doesn't mean that these people act on it, just that they have to agree with it. It doesn't even have to be in the book, if they think it's in the book, then they have to agree with it. Plus there's a huge divide between what they beleive and how they act. Every muslim I know in one way or another lives in direct contradiction with what they believe to be the word of god.
As an aside, I grew up muslim in Pakistan with a very religious father in a big household. Whenever he was around I had to pray 4 times a day in the mosque(I couldn't be bothered with waking up at dawn), and so did every other male in the house. But when he was around, we did fuck all praying unless it was a Friday. And that's how the majority of the population was in my city. Muslims are supposed to pray 5 times a day at the mosque, but the turnover on Friday's 1 prayer was 100x more then every other day. Likewise for their holy month of ramazan, the turnover was 10x the usual for regular days, and 50x for friday prayers.
Moreover, every muslim i've known had their own religion. By that, I mean while they agreed on some of the wider principles, there was always a lot of points of contention where people disagreed and had their own beliefs. For example, one of the guards we employed was a northerner, an area which is renowned for being quite radical and backwards. Now he argued that smoking cigarettes was haram, i.e. a cardinal sin, on the same level as alcohol, which is a HUGE no no. BUT, that region of the country is renowned for it's production and consumption of hash(weed). The region is a breeding ground for extremists, but go around there and you'll see people lighting up on the streets and in restaurants. It's so prevalent that at some establishments you can tip in hash instead of cash. And go to any other part of the country and hash is on par with alcohol and a massive taboo.
TL;DR Everybody believes what they want to believe, nobody's read the book they swear their life by, and very rarely do people actually act on what they believe in.