If you kiss on the first date and it's not right, then there will be no second date. Sometimes it's better to hold out and not kiss for a long time. I am a strong believer in kissing being very intimate, and the minute you kiss, the floodgates open for everything else.
Someone able to carry on a conversation whether the topic is silly or serious. Knowing enough about life so that you always have something to say is a definite bonus.
People could rationally decide that prolonged relationships take up too much time and effort and that they'd much rather do other kinds of things. But most people are afraid of rejection.