From the article:

"Higher wages were necessary, Ford realized, to retain workers who could handle the pressure and the monotony of his assembly line."

So in Ford's case, he was simply paying the going rate. Supply and demand. The lower wage wasn't enough to keep the workers he needed in his revolutionary assembly line. People spin this all the time to say things like: "He increased the wage so his workers could afford to buy his cars" But if it were as simple as that, he could have tripled or quadrupled their wages so they would buy even more or at a quicker rate.