Accounting and bookkeeping. Unlike the average person, businesses deal with the iron fist of government bureaucracy, not just to stay compliant, but to even open shop. So when a business that's already stressing out about tax filing adds the extra headache of when Bitcoin was accepted and when Bitcoin was given out and does that count as taking profit or as a gift and what was the price of Bitcoin at each time and oh no I need another point of sale to even accept Bitcoin and that means I have 2 systems for accounting and AHHHH

Hopefully when square adds Bitcoin this will no longer be such a barrier.