command lines are powerful, but only make sense for power users because they lack discovery and require more memorization than GUIs.

Simple voice interfaces suffer the same problems as command line interfaces while being less flexible and slower to use than even GUIs.

The best voice interfaces have made good progress on most fronts, but discoverable voice are still a big problem. Instead of reading a bunch of buttons, you usually have to guess what features might be implemented. Or you go the route of phone system menues, but everyone hates those