This is just my personal opinion.
I couldn't another thread where this issue is being discussed.

China (esp. Shanghai) is moving away from a cash to a digital money economy.
While foreign cards were always a problem, cash was usually king - for a long time.
However, recently most shops prefer payment via Alipay and Wechat Pay. This is a problem for foreigners, because setting up Alipay and Wechat Pay is a hazzle.

I am not 100% sure about that, but usually you'll need a Chinese mobile number (not a big problem) and a Chinese bank account (a big problem) to fund the payments.

Without Wechat Pay and Alipay:
- You cannot hire any bikes in Shanghai
- You will have trouble ordering or finding a taxi
- Traders look in a weird way at you, when you try to pay with cash.

My fear is that the Chinese Government may do away with cash within the next 3-5 years.