Why doesn't Chinese mainland often use the traditional right-to-left layout?

This question is only discussed with calligraphers and may not be accurate. It should be a change in writing tools and writing conditions. Vertical writing and right-to-left writing are the continuation of bamboo slips' writing habits. Generally speaking, the left hand holds the bamboo slips and the right hand holds the pen, so the writing is naturally vertical, but the content recorded in the bamboo slips is limited. How to place the finished bamboo slips without disorder is a problem. It is more natural and convenient to arrange the note from right to left from the point of view of taking and placing the note with the left hand. After that, although bamboo slips were replaced by paper, for a long time, the writing style remained in the form of holding a scroll and a pen. Although there were many records of writing at his desk in Wei and Jin Dynasties, every Rainbow learner held a bamboo slip in one hand and a pen with three fingers in the other. And writing at the desk, the brush is also hanging on the wrist, which direction to write will not have any impact, and it is naturally the best choice to continue the habit. After modern times, the appearance of hard pen writing led to the writing posture can no longer be suspended, horizontal and left will not let the hand touch the ink. At the same time, due to the large number of foreign languages in daily writing, horizontal arrangement is more suitable from the point of view of printing and writing.