Why does a cow always seem to chew something?

It's probably because that's all you've ever seen them do, especially if you haven't the time to watch these animals for a much longer period of time than when they're laying chewing cud. The reality is is that they only chew cud when they're resting, or ruminating. Chewing cud is just a ruminant's way of further breaking down the feed that they had swallowed whole and needs to be rechewed again. When this step in ruminant digestion is complete, the cows go back to eating again.