Why the returns are the problem, not the proof
A profitable business run by a competent accountant is supposed to show less taxable income. Depreciation, equipment purchases, vehicle and home-office deductions and retirement contributions all reduce the number at the bottom of the return. The owner experiences a good year; the return reports a modest one.
Agency underwriting reads that bottom number. So the better the tax planning, the worse the file looks, which is the opposite of how the owner understands their own business.