Why were the muslims not able to conquer most of the continent?

For the particulars, it depends on the continent in question, but usually it was because of the military strength of Non-Muslim Countries in resisting conquest.

the answer is

most people now work in jobs where they do one  kind  of work; they are carpenters, bankers, cooks, mechanics, and so forth. likewise, most  businesses produce  only certainkinds  of  goods  or  services, such as cars, tacos, or gardening  services. this feature of  production  is known as specialization.