The awt TextComponents TextField and TextArea give editable text areas with automatic border decoration. On motif/X systems, this decoration is a border shadow surrounded by a text focus indicator. I don't know what it is for Windows or MacOS, but I suspect that the versions for those window systems also have decorations. There's no way to make a text area without these decorations.

There are several instances where text areas without the default decorations are desirable: when an entire window is a text area; when many text areas are presented in an array like a spreadsheet; when it is desirable for a label to be "Copy"-able without it being editable or necessarily having a cursor or gaining the keyboard focus; and when the programmer wishes to provide his own border decoration.

All three of the Window systems (Motif/X, Windows, and MacOS) support text areas without decoration in a fundamental form. In fact, on Windows and MacOS I believe these are easier to implement than decorated text areas. So there's no "portability" reason why this should not be implemented.