Maybe bec there were times they couldn't develop enough, due to oppression and invaders in their countries?
Or maybe bec the Hollywood film industry depicts them as such!
In reality:
When Europe was still in the dark ages; the Muslim Empire was flourishing and going trough it's Golden Age. Christians, Muslims and Jews were living peacefully together. It's true that Non-Muslims were paying jizya in exchange for safety and protection; but what the heck...? Nowadays people are also paying taxes and stuff!!
Sir Mark Syce, writing on the qualities of Muslim rule during the period of Haroon Rasheed said: "The Christians, the idolaters, the Jews and the Muslims as workers running the Islamic State were at work with equal zeal.":
http://www.irfi.org/articles/articles_401_450/golden_age_of_islam.htm
The next video shows beautifully the immense contribution of Muslims to this world. Three school children visit a dusty library to research the story of 'The Dark Ages'. What they find changes their world view dramatically as ingenious inventors and pioneers of science and culture are vividly brought to life.
https://www.youtube.com/watch?v=JZDe9DCx7Wk
The Lost Kingdom Al-Andalus:
The Islamic Golden Age is a historical period lasting from c. 750 CE to c. 1257 CE, during which philosophers, scientists and engineers of the Islamic world are credited with a period of contribution to scientific knowledge, cultural arts, civilisation and architecture, both by developing earlier traditions and by a period of relatively rapid and marked innovation. A substantial degree of historic Islamic intellectual innovation occurred in the Islamic Golden age, and it was this which helped to bring Europe out of the dark ages and brought about the resonance (rebirth) of Europe, Islam brought the light back into a world of darkness:
https://www.youtube.com/watch?v=bbTXRCbLArE
Muslim inventors that changed the world:
http://www.independent.co.uk/news/science/how-islamic-inventors-changed-the-world-469452.html
What Was the Islamic Golden Age?
By the 10th century, key Islamic cities such as Baghdad, Tripoli, Cairo, and Cordoba had huge libraries with between 600,000 and 3 million books, many of which were destroyed in subsequent centuries. The corpus of knowledge generated during this time exceeds the combined works of ancient Greece and Rome, and represents the first scientific works in history. Fundamental findings in optics, mechanics, physics, agriculture, chemistry, mathematics, astronomy, and thousands of other fields were achieved during this time.
http://www.wisegeek.com/what-was-the-islamic-golden-age.htm
During the Golden Age Muslim scholars also made important and original contributions to mathematics, astronomy, medicine, and chemistry. They collected and corrected previous astronomical data, built the world's first observatory, and developed the astrolabe, an instrument that was once called "a mathematical jewel." In medicine they experimented with diet, drugs, surgery, and anatomy, and in chemistry, an outgrowth of alchemy, isolated and studied a wide variety of minerals and compounds.
Important advances in agriculture were also made in the Golden Age. The 'Abbasids preserved and improved the ancient network of wells, underground canals, and waterwheels, introduced new breeds of livestock, hastened the spread of cotton, and, from the Chinese, learned the art of making paper, a key to the revival of learning in Europe in the Middle Ages:
https://www.islamicity.com/mosque/ihame/Sec7.htm
The Islamic Golden Age, also sometimes known as the Islamic Renaissance,[1] was traditionally dated from the 8th century to the 13th century,[2] but has been extended to the 15th[3] and 16th[4] centuries by recent scholarship. During this period, engineers, scholars and traders in the Islamic world contributed to the arts, agriculture, economics, industry, law, literature, navigation, philosophy, sciences, and technology, both by preserving and building upon earlier traditions and by adding inventions and innovations of their own.[5] Howard R. Turner writes: "Muslim artists and scientists, princes and labourers together made a unique culture that has directly and indirectly influenced societies on every continent."[5]
