Don't compare so one-sidedly. Manual workers may earn more money but do you know what they have to go through? They have to work 10-12 hours under the hot sun or pouring rain, they do hard work and almost non-stop, or worse, they can have an accident and lose their life at any time. Not to mention, the job is unstable and can be fired at any time, they may have financial difficulties.
Meanwhile, as an office worker, you get to work in an air-conditioned environment, enjoy full insurance, salary, annual leave...not to mention, you will have the opportunity to be promoted with a better salary.
I don't know if there is any difference between our countries, but in my country, most of the poor people are those who have no education or degree. People with degrees may not always find jobs in their field of expertise, but they do not lack job opportunities and can come up with their own business ideas using the knowledge they learned in school.
Construction work is a very unpredictable, hard and hard to understand profession. About 15 years ago, regular helper without experience (bring this and that, hold this, clean and all such kind of work) earned +100 EUR per day, while employee with MBA earned 30-40 EUR per day working in a bank. There are exception in every job. I've seen young men working on a construction for 3-5 days per week, and I cant tell that they were killing themselves working, as there were days and hours when they do nothing. And I saw people working as a manager in bank for ~5 years without promotion, whos job talks with clients and solve their tiny problems with payment.
In my country, poor and without job are people who are either lazy or who say "I am not doing it for this amount" (and they want to earn highly above average salary straight from start), and not who are without education or with it.