Yes you are right! Morocco was actually really wealthy compared to all the African States in the 19th century, and because of this it made it past the initial "Rush for Africa" after the Congress of Berlin in 1878.

But Morocco was too internally weak to fend off the hydra of imperialism forever. It was not nearly as centralized as the European Powers. The defining factor though is the industrialization of the european states. Yes, Morocco was rich. Yes Morocco had comparable technology (to an extent). But Morocco did not have the industrial might to compete with the European.

Morocco was annexed not really by force but by the threat of it. Moroccans knew they could not win a war against France. Imperialism often worked like this: capitalists or the government would invest or create trade in the country, then would find cause to have to "protect" the industry, and then eventually demand and threaten war to set up some type of economic concession to protect "economic" interests in the country.

It was by these means that France justified establishing a protectorate over Morocco. In 1911 a rebellion took place against the Sultan, and the French volunteered to help bring down the riots, but the occupation of the French troops ended the self rule of Morocco. The Treaty of Fez recognized this diplomatically!

Sources: Kishlansky: Civilization in the West