The problem is that reducing costs doesn't typically scale. If you want to grow a businesses profit significantly, you need to increase sales. It's entirely reasonable to double your sales. It's pretty difficult to halve your costs.
Or do a mix of both. Doubling sales multiple times is more likely than making profits on your infrastructure... Amazon AWS is probably the exception here.
Suppose you purchase widgets from a manufacturer for 100$ and sell them for 101$. In that case, 101$(revenue per widget) - 100$(cost per widget) = 1$(profit per widget). Suppose you then change manufacturers and reduce your cost per widget to 99$. You now make 2$ profit per widget. By reducing costs by 1%, you doubled your profits. Much easier than doubling your sales.