Because 'get to work' is a point event– it happens at, say, 8:59 am– while arguing is a durative event– it happens over time. So these are the ways a native would instinctively form these verbs, unless context or intent suggested otherwise. 'they always argue' is also possible, but it makes the action more 'distant' more a generality and less an activity. 'He's always getting to work on time' i