Why didn't pre-Gutenberg movable type systems cause a printing revolution?

There are a couple of issues here:

1. Writing system.

Moveable type printing gives the greatest efficiency gains when the writing system doesn't need to employ a lot of different glpyhs. This means it works much better for systems that are alphabets (30ish glyphs) than for systems that use syllable glyphs combined with logographs (tens or hundreds of thousands of glpyhs).

So although the Chinese had worked out, their quasi-logographic writing system meant that making industrial use of it for the traditional Chinese writing system would require pre-creation and organization of what looks to western eyes like a completely unreasonable 50,000ish glyphs. For the modern Chinese used for newspapers today, the count commonly used is reduced to a mere 3,000, but that's still two powers of 10 more than that required for German.

You might think Korea was in a better spot here, since their modern writing system is quasi-alphabetic. However, that system was not invented in 1377 when their press was. So their press used a system borrowed from Chinese (or rather, it used the Chinese writing system), so it had the same problems.

2. Literacy

This one's tougher to get good numbers on. There seems to be a recent trend to up-estimate Europe's literacy during the late middle-ages to possibly as high as 40%. Certainly the influx of paper to the region starting at the 11th Century attests to an demand for it existing. If those high numbers are anywhere near accurate, its quite likely the relative simplicity of its alphabetical writing system played a part. Clergy and monks were likely nearly universally literate.

For China the estimates I'm seeing are more along the lines of 16-30%, but in China literacy wasn't so much a boolean thing, but rather measured in the number of glyphs you know. So a barely literate Chinese person would perhaps know only a few hundred characters, while the full system contains on the order of 50,000. I don't have any info for Korean literacy at this time, but as they were still using the Chinese system, it seems fair to assume it wouldn't likely have been much better than the Chinese were experiencing.

I don't want to overstate the case here. Chinese is printed today, so its still an improvement over not doing so, and they continued to do some printing back in the day too, so it wasn't a total waste of time then either. However, when a tech is new its going to be at its least developed and efficient. At that time, there simply wasn't nearly the gain to be had for printing over professional hand-copying in China or Korea that there was in Germany.

"Why" questions are notoriously difficult, and I am sure there will be plenty of scorn piled on me for even trying...

Any major invention consists of many parts. It also requires a market to take off. Let me start with an example that I'm more of an "expert" on - airplanes.

The Wright brothers are rightfully credited with its invention because they invented the final piece - the 3-angle control system (their predecessors' planes took off and fell down because they failed to control them in all 3 directions). Also there was a ready market for airplanes - militaries needed them for reconnaissance (even though generals did not realize that yet).

I suspect that the lack of economic success of movable print invention in China is a combination of technical and economic issues.

Movable print consists of many parts: reusable metal letters, matrix, ink that dries fast but can be removed from the letters &c. The letters must be simple enough so that inevitable imperfections and fouling do not make the printed text unreadable (a problem with the 1000s of Chinese characters).

The market requires a big pool of literate people who need the book. Remember, it is faster to make 1 copy of a book by hand than by printing, so to justify printing it, one has to know that there will be many people buying it. Europe had Bible that everyone wanted to own. Did China have a text of similar importance that everyone wanted to own? How many characters an average literate person knew? How many people could benefit from owning a book?