Look at their backgrounds - large number of them were lawyers and judges, several of them were merchants, surveyors, farmers, scientists before entering politics. Engaged in securities, land ownership, diplomacy and local constitution writing. All highly qualified for the time and unlike career politicians had extensive experience in other areas. Combination of political experience and experience from different areas and backgrounds led them to write that document.
I personally find most politicians today to be wholly unfit. Not just in the US but elsewhere. A lot of them are career politicians with minimal experience outside of politics. You see a lot of people jump from university into the political bubble hoping to become a person in a position of power in x number of years. Rarely do you get someone with extensive outside experience. It is one of the things I liked about Trump when he ran, and was used as a point against him. You are not a career politician, you don't have political experience. No, he just has extensive experience in the New York real estate market before the mob was cleaned out, as well as extensive in media and television among other things. What does Joe Biden bring? Law experience 50 years ago where he worked in a political mill firm with strong Democrat party ties before becoming a senator in 1972? What does AOC bring? Bartending, waitressing, book store owner? Even slimeball Mitt Romney spent most of his life doing business, management consultancy and private equity, he has more outside experience than Joe Biden.
Government should be led by people with extensive experience in different areas, not career politicians who jump onto the machine and bring very little to the table. It might sound elitist, but it's not, it's anti career politician.