Why do some stocks have a pre-market value whereas others do not?

When the pre-market opens, if there are no participants at that time offering to buy or sell stock then there is no activity and the stock remains at the previous day's closing price.

When orders are placed by market participants, the bid and/or ask price may change and when counterparties agree on price, transactions occur. If there is an aggregate net buying or net selling that takes out the orders at current price on the order book, price will move up or down.