Patterns in cross market liquidity

Academic research on liquidity has generally focused on explaining what can be called within market liquidity. That is it seeks to explain things like why one stock is more liquid than another. But there has been considerably less attention to cross market liquidity: the issue of why some securities are more liquid than others. For example, stocks are apparently far more liquid than high yield bonds. Why? Why do some markets exist (orange juice for example) while others do not (potatoes for example)? This article lays out the current academic evidence regarding liquidity across assets and explains why current theories have trouble with one item or another. The challenge then is to produce an overarching theory that offers predictions that are closer to what the data seems to imply about cross market liquidity.