It is taken from the fact that the masses with poor quality of life under the old system became the majority of participants in the radical and belligerent response to the French Revolution. The picture shows their common clothes. The most fundamental political ideals in the early days were social equality, economic equality, and direct civil rights. Excessive heat began to quickly lose support within the National Convention.
The reason for adopting this is also to state that although you can freely express your inner thoughts in the free world, it is not good for anything to go wrong! The process of promoting the free world in the early stage is helpful, but then you must find a balance to live comfortably in this democratic society.