The issue is with data movement, in my opinion. Heavily pipelined command languages like shell and stack languages tend towards unreadable because they perform

The issue is with data movement, in my opinion. Heavily pipelined command languages like shell and stack languages tend towards unreadable because they perform actions on arbitrary data with implicit transfers between functions, which can be confusing to the uninitiated, because you have to know every (not necessarily obvious) command and it's parameters beforehand.