Crawl Space Repair - New Joist on Right, Old Joist on Left

In this picture, you can see that there is a fairly new wooden subfloor joist on the right and an older, mold covered one on the left. What this tells an inspector, and our crawlspace experts is that the problem with crawlspace moisture has been going on for a very long time and the root cause of the problem has not been remedied. What is the root cause? Check out the next picture.