Chances are, you live in what is called a "Right to Work" state, which allows your employer to legally fire you if you ask for a raise at all. Most employers won't do this, of course, but the fact that they can harm your family finances this severely on a whim creates a power imbalance that emboldens them and infantilizes their employees.
When workers organize a union, they are protected from this kind of abuse by a network of laws and statutes. When union workers go into contract negotiations with an employer, they will not walk into their bosses office, hat in hand, to humbly ask for a few more cents an hour. Union negotiators, which include representatives from the work floor itself, will come into the offices with lawyers, and a team of experienced union deal makers. A union can force the Company Bosses to open up their financial records and prove that they really can afford fair wages, or sick time or vacations.