From month to month Alexa rankings of websites move up and down, especially those with rank in the hundreds of thousands and greater. Longer term rankings will change as more sites come online even with the same activity at a site. Here are the rankings for genealogy sites at the end of 2014 and 2015, and the percentage changes calculated so a positive change accompanies a more favourable ranking.
All the major commercial sites, and FamilySearch, saw double digit percent increases during the year. By that measure genealogy is thriving for the major online companies. Another site, trafficestimate.com shows similar trends with visits to familysearch.org up 18.5% year over year, ancestry.com gaining 27.5%, findmypast.com up 90.3%, and myheritage.com up 44.2%.
The situation is mixed for non-profit genealogy societies which show the largest percent gainers and losers. As long as a society website continues serving its members trends should be of less concern.
I'm not sure what to make of the 50% +/- 20% percent declines for several blog-like sites, including this one. Could it be an impact of social media?