Because they get screwed more than anyone else at every other level. They are paying the same real property taxes, business personal property taxes, state taxes, etc, and now Obamacare taxes, that the larger companies pay, but without the economies of scale benefits. If a public company is paying a 4% combined real and business personal property tax rate on a 100,000 square foot plant that provides them with a 16% profit margin, that is a much lower burden than a small business paying that same 4% combined rate on a 20,000 square foot plant that gives them a 9% margin. So if you want to say that's their problem then okay, but you end up with a nation of WalMarts, which I think most people would like to avoid.
One other thing - I don't view accelerated depreication as a benefit. In most cases it serves to be an cashflow anchor for a lot of businesses. The equipment purchase is usually financed, so in years 2-5 the loan payments still need to be made, but there is no deduction other than the interest. So if the company has $32,000 of taxable income generating a $10,000 tax bill, but $25,000 of principal payments on the loan, then the company has a negative $3,000 cash flow. Yes, they got the benefit in the first year, but 9 times out of 10 that money had to be spent on other things, not socked away. The biggest problem most small businesses have is focusing on income instead of cash flows, because that is the way our tax system forces them to think. In the absence of my preferred overhaul of the code to focus on consumption (cash flows) as opposed to income, I would prefer an option whereby the business owner could tie depreciation dollar for dollar with the loan principal paydown (but only if a standard amortization of the loan to keep it simple).