Why should you never buy A-shares?

Because you can't short them.
This is a systemic problem.
Short sellers are like woodpeckers on trees, able to peck out pests.
Foreign stock markets allow short selling freely; if short sellers believe a company is worthless, they will drive the stock price down, leaving better buying opportunities for retail investors, and capital naturally becomes more confident to buy.
At the same time, the battle between bulls and bears causes more intense volatility in the short term, but in the long run, it is very smooth.
A-shares cannot be shorted; the bulls drive the company's P/E ratio to 1000, then hand it over to ETFs, funds, retail investors, etc., to take over.
No short seller can restrain the reckless speculation of the bulls.
Therefore, A-shares often experience A-shock, which is literally reflected in the name.
Because the bulls must realize profits and sell off, and once they sell, A-shock occurs; no early bulls can survive.
If there are short sellers, then their selling during A-shock is just giving money to the short sellers.