Well it turns out that the tradition of not picturing Mohammed is a relatively recent one - one that really only appeared in the 1600's. So for almost a thousand years after Mohammed's death, it was acceptable and even common in some Muslim regions to draw him in full form. During the Caliphate period there were even coins minted with his face on them. Even the burqa which has become a symbol of traditional Islam didn't appear until after Mohammed died and was until recently confined mostly to women in the harems of the aristocracy.
A lot of behavior that radical Islamists insist on today in western countries are actually traditions that got added to Islam long after it was founded. So to make a stretched analogy - it's as if the Amish somehow got control of Christianity and decided that the fashions and practices of the 1700's define how a true Christian must act today. And threaten to kill you if you dare disagree.