This simply isn't true, outside of large chains or supermarkets. Many smaller businesses like pubs, "kiosks", barbers, non-chain restaurants, and so on, are cash only.
It's a combination of tax avoidance and trying to avoid the insane level of paperwork needed for bascically every aspect of life, but especially if you have a business, no matter how small.
Source: live in Germany, near a large metro area.