What exactly is easier about auditing profits, when they are the difference between a claimed number (income) and another claimed number (expenses), whereas sal

What exactly is easier about auditing profits, when they are the difference between a claimed number (income) and another claimed number (expenses), whereas sales tax is literally printed on receipts? Thats why you hear about megacorps paying $0 in (profit) tax, but you never hear about anyone "dodging" sales tax.