Traditional, procedural programs have a single order of execution. Control moves in a linear fashion from the first statement to the second statement to the third statement and so forth with occasional loops and branches. User input occurs at precisely defined points in the program. A user cannot input data except when the computer is ready to receive it.
This doesn't work well with GUI programs. Users can select menu items, type text, click the mouse, or otherwise provide input at almost any time. They have many, many choices at any one point about what to do.