乐谱 Chinese music tablature
There are three points why 简谱 prevails in China.

Tonality.
Most music pieces are tonal music. And 简谱 is essentially a &quot;movable&quot; do notation system, which makes it easier for reader, esp. amateur, to grasp the melody.
History reason.
In Chinese traditional music, 工尺谱 is the main notation system, which is comparable to 简谱. 工尺谱 is also a &quot;movable&quot; do notation system.
Culture. (Why 1, 2, 3 not C, D, E)
Chinese is more familiar which the order of number than the English alphabets. Using Arabic number makes it easier for beginners in China to establish mapping from 1, 2, 3 to do, re, mi and easy to spread and learn. I don't think it has anything to do with the rejection of alphabetic characters.

The use of 简谱 was common in Chinese traditional instrument performance. But now conservatories in China use staff more. Now 简谱 is more common in music score for amateurs (esp. guitar scores, or chorus scores).