purplekitty - 8:50 pm on May 19, 2013 (gmt 0)
Yeah, theoretically it could be anything since no one but Google really knows anything for sure. The anchor text idea is the first time I'm getting that suggestion.
Anyway, I'm very analytical in my approach to things and so I tend to look at things based on probabilities.
Looking at the knowns, using WMT, I know who's linking to me, how many links, what pages, etc. and I know what anchor text is being used.
I also know what I've been doing, that I've ranked for these terms in Google for years, and that I continue to rank in both Bing and Yahoo for these terms fairly well on average (obviously some better than others).
Additionally, I haven't received an unnatural links message from Google and I know that I don't have a manual penalty. The only message I've received from google is that I had a large decrease in traffic for my top url (or some such, I don't remember exact verbiage) that I received for both websites, a few months apart, after my rankings for the top keywords vanished.
While I always leave the possibility that I'm wrong because clearly I don't know anything for sure, the only probable explanation of all suggestions thus far is that Google sees me as a link farm and that I have some type of algo penalty applied by Penguin.
The ways I might be able to correct that (if it's that) would be to remove all my links to my other website (which is not feasible since they're there for my users and have value) or nofollowing them (which I've done).
Admittedly, what I think is going on is only an assumption, but it's not a blind assumption. It's based on logic.
If it turns out to not be that, then I have no reasonable idea what it could be. As I've mentioned before, I'm not saying I should rank #1, or even on the first page, for any particular keyword, but to no longer rank at all for some popular phrases that I previously ranked well for defies logic unless you consider that I've got some type of algo penalty being applied for some reason.