Because one gains more from any experience wherein something in the way of effort is demanded. A beautiful vista is more sweet when it takes effort to get to it. A relationship with a person is more fulfilling when trials and tribulations are overcome together. Hard won knowledge imparts a deeper wisdom when it is obtained in spite of difficulties. You would like to believe your child understands concepts from videos because it makes you feel good, but I doubt you are going to have him build your deck. Intentional effort is a prerequisite for deeper fulfilment. While there are things that are better demonstrated via flashing images, there is no substitute for the cognitive effort required to read deeply on a subject, or follow a rich and complex narrative.