The problem for me with personalization is that it's annoying to always see the same set of things. For instance, I'm mostly a Python programmer. But I've found that if, for instance, I'm subscribed to the Python reddit, I get too much Python-related content in my news feed. That's not really my focus -- I'm really a programmer first, and a Python programmer second. I'd rather see interesting programming things -- regardless of the language or focus -- than I would in seeing Python-related content.
As anohter example, I've found the same is true with political stuff, which I've mostly tried to handle using RSS feeds. I can subscribe to political content that I'm interested in, but then I find that I just end up reading the same things and viewpoints over and over again. I'd rather read political content that's interesting and well written -- regardless of its political stance -- than I would read political content related to some sort of viewpoint or interest. That's the value of a "logged out" reddit/hacker news, or the front page of a newspaper; I'll see the most important things first, and then do my own seletion of whether or not I want to read the stuff contained therein.
One interesting sidenote is that reddit basically dropped the personalization filter thing a long time ago. You may recall that they used to have a "recommended" articles tab, which was supposed to learn about what you were interested in based on your voting history, and then by clicking on the tab you'd see the top articles that it thought were relevant to you. AFAICT this feature no longer exists, and now they just have the sub-reddits system where you get a simple mix of content from subreddits you're subscribed to. I'm not sure exactly why they dropped that (it never worked very well), but that might be something to ponder a bit.
On the other hand, it could be that you are upvoting not things you want to see, but things you agree with. Tragically, many people do. In that case, it's your own fault (or the fault of anyone who does such upvoting, and dislikes the results); the personalization algorithm is doing it's best, but it's getting bad data. And since upvoting based on agreement is so common, this also might answer the OP's question.
One reason might be that the existing range of news portals is good enough for most people to get approximately personalized content. People can find one or more news outlets, aggregators, or blogs that more or less reflect their interests, whether it's HN, Reddit/Subreddits, Slashdot, CNN, Fox News, DailyKos, Lambda the Ultimate, or whatever, and they just read those, supplemented with links passed on from their friends via Twitter/Facebook/etc. So your market is the people who can't find any combination of those that works for them, which maybe isn't a ton.
A different reason might be that Google News does personalization (via the "Recommended" box), and so already captures a decent part of the market for news personalization, at least in the newspaper-articles sense.
A third might be that it's hard to do well. To really catch on, people need to rarely get articles they don't care about, and often have this feeling of, "yes! this is exactly the kind of news I want to read, and which I wouldn't have found otherwise". That's probably hard to do! The Google News recommendations don't really blow me away, for example, even though I've been using it long enough that it should have decent data by now.
So I think it is a hard problem, as said here, serendipity is hard to program. However, I am absolutely sure we have not yet figured out the best way to browse. Search seems pretty good, but internet browsing can easily be too time consuming and aimless.
