Given how USB sticks are usually meant to be portable and plugged into different machines, possibly different OSes or installed programs. This makes it realitively more cumbersome in terms of usability for encrypted USB sticks. And I believe this is the biggest reason why people do not encrypt their USB sticks.
Since all discussions I found about encrypted were years ago with few comments, I would like to ask HN what is your preferred way to keep your USB encrypted/secured?