To give a simpler answer, not all profit is income. let's say you own a small company and you earned 100k of profit in a year. If you want to take that 100k as income and pay yourself(the owner), you're going to get taxed pretty high. But instead you could really use a new work truck, so you buy a company truck that goes as a business expense and pay yourself the remaining 50k.
Companies have a lot of options in ways to spend their earnings without it having be taxed as income.