Nothing at all, except most businesses still have input costs, and taxes to pay, in shitcoin. Also, a lot of business is built on people's word, trust and credit - which has it's own value. As such, much of business is in fact fiat. The problem is, we've allowed business to = money. While both are considered capital, Business ≠ Money. Rather, business allocates money. So, fiat can be used for business so long as you're measuring results in Bitcoin.