Why our published items are mainly written [documents.]?

Streaming video on devices consumes lots of bandwidth and energy. In some developing countries, internet bandwidth and electronic devices energy are still expensive for some sections of the population.
Therefore, we prefer not see these sections of the population left out of the possibility of learning and self-improvement.
With the written materials, anyone can download them once on their devices and use them many times over, without consuming unnecessarily  their Internet data allowances.
Another case would be for schools teachers, in less affluent areas, to download copies of some StudyNotes by [OxfordCambridge.], and then make them available locally to pupils and students, in their schools' physical or digital libraries.