Why should we look for coins with large trading volume?

Trading volume is always the most important parameter. No matter who buys the coin, if the trading volume is only two or three million u, don't buy it. It's basically a case of mutual profit.

The larger the trading volume, the larger the gaming group, and the higher the probability of making money.

To put it in the most extreme way, if only two people trade, then either you lose or he loses. If the trading volume is already large relative to the market value, then the money you earn may belong to other trading players, rather than a small number of people cutting each other.