There are some organizational quirks to how the code is written. It has been around for a long time, so it still has some design elements from working within older Java versions. Like many projects it is reliant on integration tests, likely more than would be desirable.
As far as the wider Apache ecosystem, I know there are projects that get by with pretty low code quality. Unfortunately there aren't many central voices at Apache enforcing specific policies around how codebases are managed, they are more focused on community development. I think they may be better off trying to take a closer look at codebases during incubation. Then again, there is no excess of resources waiting around to review code, and a lot of budding communities that want to take part.