DG:
To make money for the owners. I've been self-employed and a multi-business owner since the late sixties.
A better question is why does society allow businesses.
Warning - Now we're going to get into capitalism and free enterprise that wingers don't appear to have clue #1 about, confusing both with banana republicanism, ie; Rich folks own everything and provide jobs to peons at the lowest possible wage consistent with making more money.