In fact, they may prefer it. Small legible writing is often that of an intensely focused person. They are more comfortable on the mental plane than the physical one. Small writing may also indicate a humble, reserved person. They may prefer working alone rather than in a group.
Some people say their writing changes all the time.
Most often the slant of their writing will vary as it is the one area so easily effected by changes in emotion. The more writing slants or leans to the right, the more quickly the writer will respond to emotional situations. An impulsive person will have writing that slants very far forward with little controlling traits such as pride, fear of disapproval, or caution. Jacqueline Kennedy was known for her grace and poise. Although the strokes in her writing measure from left of vertical to far-right, the overall near vertical appearance reflects the air of composure she so often exhibited in public.