Working or living in europe, impossible?

So I did alot of research ( A Lot) on obtaining EU citizenship and I understand that it is next to impossible unless you marry an EU citizen, have a medical degree, or for some countries have a close relative that came from there like a grandmother. Im curious as to why it is so hard for an educated Canadian or American to get citizen ship, yet most European countries have over 10% of their population comprised of immigrants, and most seem to be from countries china, south America and the Arab world....now There is no way you can tell me that all these immigrants have high demand skills, like doctors and Computer software experts, so why is it so hard for a Canadian or American to do this, yet there are people immigrating from china to open little restaurants and people from Syria immigrating and driving cabs. Is a cab driver a high in demand job? lol. How do these people do it? how are they getting into Europe with out medical degrees and what not, yet its impossible for me a Canadian with a civil engineering degree?