Typing Chinese is significantly harder than typing English. Thus, voice memos offer a superior user experience. Building in Voice Memos as a first class feature into the messaging UI was what got WeChat its initial push.
Let's say you wanted to write 我很喜欢吃汉堡 (I really like eating hamburgers), you can get away with just typing 'w h x h ch han bao' and predictive text gets you the entire sentence.
Chinese text is well optimized towards readability and information density, at the expense of taking a lot of work to manually write, but that calculus completely changes if your writing system is smart enough.
I think voice messaging took off in China mainly because they don't have the same cultural barriers to voice messaging that we do.
I love China, but I do believe the culture of apathy towards others that are not family have helped this. 没办法！