I would say that they play slots not because they are lonely, but because slots is an easy game. You dont have to do much, insert money, pull the lever and wait. You dont have to even think much, just sit, pull and wait. Imho such easy-to-play games are what makes people addicted, because entrance level to it is as low as possible. With online it is even more easy. Even though people gamble online more now, offline casinos and slots in particular made mode addicted gamblers than ever.