Good point, programming is much about communicating not only with the machine but with other people. Writing serially executable code is a bit like explaining to others and yourself what you are doing there. If instead we have a "wire-frame" of a program it presumably naturally calls for some kind of explanation. Explanations need to be textual because humans communicate textually. Humans prefer to give each other instructions textually, not as graphs, because less interpretation is needed with strictly serial text.

Visual programs are a bit like if you were presented a program which needs to be read from bottom up right to left. Would that be somehow easier to understand? Visual language presumably can combine both left-to-right and right-to-left and up-down and bottom-up interpretations. While it's possible that such model would be more expressive than conventional programs, that is not certain to be so from the outset.