One reason that today's preschool teachers don't emphasize to their children that they must color within the lines of a coloring book (as teachers did a generation ago) is that a. large-muscle control is necessary for this activity. b. preschoolers don't like the structure of a coloring book. c. preschoolers have problems with this type of coordination. d. it is considered creative to color outside the lines.

The answer is: c. preschoolers have problems with this type of coordination.

Option C is the correct one because preeschoolers are not developed enough yet to have that capacity.
At the age three to four, the child will try to color within the line but there won't be much success.
When they are around five years old, we can see coordination between the fingers and wrist, and they start to show what hand is going to be dominant. By the time they are six, all of this should be apparent, consistent and they should be capable of staying within the lines.
Teachers from a generation ago, did not knew about this and would pressure the kids to do something they were not ready for.

The educational system today have already evolved where preschool teachers do not anymore emphasize to their children that they must color within the lines of a coloring book because it is already considered creative to color outside the lines. Students are now push to innovate and create ideas to break the barriers of controlling their capacity of creation.

 

That would be a working theory.