But why do people say never buy?
Its not possible for people never to buy, it is only advised that you should speculate well before investing, in such a way that your entry point will always be when the market is dip, this will help you to be more profitable about your investment, then you can from there hodl till you feel its perfect enough to sell.
But where is the value of BTC in the absence of trading?
trading is a continuous process with bitcoin, people will continue to buy while some are selling, this is because there is no how everyone can be holding at the same time, selling at the same time or buying at the same time, the general market is decentralized and you can afford to do which ever pays you according the the market season you find yourself.