I used to do a few hundred a month from adsense on my tutorial site. Google penalties and lack of updates and now I only see a few dollars a month. My traffic went from ~70k uniques per month to 5-10k, so it's not that shocking that the earnings went down.

Sadly the spammy made for adsense sites I had did much better than the one legit site I poured most of my time into. I think this is part of the reason so much crap exists.