I don't know whether it is foolishness or plain suicidal tendencies that causes these cartoonists to parody Islam and the prophet Muhammad in that manner. I just don't know.
The traditional Muslim mindset is simply different. Once you say 'God' or 'Allah' it is a whole new ball game. You automatically enter a frame of mind in which there is no room for satire or levity. For them 'God' and by extension his Prophet mean everything. Why no one sought to impress this on the cartoonists is beyond my comprehension. There are times when even where there is freedom of speech, common sense, sensitivity and courteousness must come into play. Some things are simply a no-no.
The funny thing is that Charlie Hebdo magazine has no interest in courting the traditional Muslim. Their target is basically regular French people and Europeanized French Muslims who understand the role satire has in politics, but even with such Muslims images like this are out of place because it make it harder for them to explain themselves to traditional Muslims why they are tolerant or forgiving of such images, and even want to associate with people who produce such images.
Take these two clips. In the first one IIRC, some journalists made some flippant comments about the Allah and His Prophet on Twitter or Facebook or something, and here is this cleric demanding that the journalist be executed. He weeps while calling for the punishment and apologizes for the state he is in. It looks comical, contrived and melodramatic, but that is the kind of cultural mindset you are dealing with. It doesn't mean that all people with that cultural outlook are inclined to go gunning people down, but it serves to show how people in other cultures can be different from you and I, the so called typical Westerner.
In the clip below a man is lamenting the suffering he has gone through in some religious strife in Baghdad. The cultural character is different. Western media outlets would suppress such an outpouring of emotion and calls to God from appearing in the news, even if God was a Christian or Jewish god. That is how the cultures differ.
Why some of this so called satirists aim to offend and upset Muslims in this manner is beyond comprehension. If they are not willing to engage Muslims and a meaningful and respectful manner they should just leave them alone, and focus on their Western counterparts. Discussion with Muslims if fine but they can do so without offensive imagery which Muslims find deeply distressing.