Because we already know from the data that minimum wage causes the poorest least skilled to not be able to find work, typically replaced by more skilled individuals. You can see the attached graph from a peer reviewed journal demonstrating this.
In addition to the data clearly showing this fact, its also common sense. Companies hire people based on the value they provide. If you dont provide enough value to be worth your wage, you wont get a job. Setting a minimum wage just makes it illegal to hire people who do not produce value great enough to be worth their hourly rate. The end result is you effectively make it illegal to hire the least skilled in society, forcing people who are already desperate and need work, and who dont make enough to loose their job entirely and be unhirable, effectively causing them to starve to death.
Obviously that is not a solution, it only makes their situation worse. Both the established scientific data, as well as just basic common sense clearly shows this.
Now how do you actually solve the problem, easy, the state pays to get these people an education or training to actually make their value high enough they are hireable at a living wage.