It's not necessarily as bad as it seems because this is relative to overall search term popularity. As more non-techies adopted the Internet, the prevalence of all techie topics declined, some more than others. E.g. Python is more popular as ever, but it's search term interest peaked in 2006, even though it's absolute search numbers increased nicely.
I don't think google do trend graphs for absolute search numbers, so one way to approximate that is to compare the graphs for competing terms using Google Trends (1). So to get a feel for how popular Python is, compare it's trend graph to say Java or Ruby.
Another factor I suspect may be relevant for Linux is that the rise of prominent distros has probably sapped away search term activity for general searches for Linux.
foss is a nerd thing. The general consumer has no idea what source code is in the first place, they often don't know what an application or OS is, they just click the thing on the screen to make facebook appear.
So it loses search percentage because it isn't becoming a mainstream concept, which is sad. People should care more about their software freedom but they don't even know what software is.
The number of people, globally, using the internet, is still on that same near exponential growth curve that the first world nations were seeing in the late 90s. It really hasn't subsided; only gone to lower income brackets.
Heck, half of the US didn't have reliable access to the web until I think 2002?
And these late adopters, they are both non-english speakers and non-technical people.
Additionally, the early adopters, let's take my parents, who had Prodigy in about 1990, are now using the web more for things like shopping and content consumption, then they did in 1998.
If they wanted to watch the latest TV show, they can do that now online, AND they know this. Compare that to 2004. That will be reflected in the search terms.
Also, there are internet phenomenons that are at the order of that which we have not seen. Psy's videos on youtube for instance; 1 ba-ba-billion+? That's insane.
So yeah, Linux is left in the dust. Also, it's much easier than it used to be - take that from someone who's been using it since 1996 (?)
I need to do a write-up some time soon of how good we have it now - for my own memory.
It isn't really left in the dust, the growth rate of tech adoption is just greater than the exposure rate of FOSS and related technologies. Which is sad, but since Microsoft is the primary conduit of traditional computing systems (and today it is Google) it is against both their interests to introduce users to open compute platforms.
I imagine what will happen is that foss and linux will pick back up in popularity over time when technology hits global saturation and the only difference is old people dying and new people entering the market. The younger crowd is more likely to inquisitively understand computers better and realize they aren't just a dumb tool to be used to view facebook.
I don't think google do trend graphs for absolute search numbers, so one way to approximate that is to compare the graphs for competing terms using Google Trends (1). So to get a feel for how popular Python is, compare it's trend graph to say Java or Ruby.
Another factor I suspect may be relevant for Linux is that the rise of prominent distros has probably sapped away search term activity for general searches for Linux.
(1) http://www.google.co.uk/trends/explore