Let's set a palatable objective

That's why i counted B Class within the quality side.

There are many "skilled" editors who think that many B articles is more important than few FA. For some editors GA/FA isn't worth the bother. The GAs are increasing faster than FAs for good reason.

Unfortunately C class is a mixed bag in term of quality while B class range from correct to near-GA level of quality. Wiki projects which don't use A class anymore have more demanding B class constraints so the gap between B and GA would less steep.