I expect that since Andrew Skurka, Brian Robinson, Ryan Jordan, Scott Williamson, Francis Tapon, Roman Dial, etc. are educated, lightweight hikers who venture through exposed wilderness areas on VERY long hikes, they will be converting to tunnel tents. Why do you think they have not seen the light yet?
If you are not exposed to something and thereby don't seek it out, you're not going to know about it. Very little literature in the States, in any of the popular magazines or websites, offer much information about tunnels. Most Americans don't go looking for information about any kind of gear outside the States, very much tending to focus almost exclusively on gear within the States. As Roger stated earlier, the outdoor market in the States is huge, so no need to look elsewhere. At the same time, with that bias towards their own gear, most Americans are going to automatically assume that American gear is superior.
In other countries the outdoor market is quite substantially smaller. It is often hard to find what you need locally. So you easily tend to look at what is available elsewhere to meet your needs. That is why so many non-Americans look at and buy American-made gear... it is by far the most easily obtainable. But that doesn't mean that American gear meets local needs. One of the biggest requests from people outside the States, especially from the UK, from Henry Shire at Tarptents was shelters that could be pitched low to the ground. Many people on the UK outdoor forums decided that the Tarptents were just not going to cut it because of the openings in the sides. Over time, Henry responded to these requests, and many of his shelters that can take harsh weather, like the Scarp and Notch, now incorporate pitching tight to the ground and solid inners. One of the reasons the Trailstar from MLD is so popular in Europe is because of its superior wind-shedding abilities. In fact, though I'm not sure, the Trailstar was not a popular seller for MLD for a long time, until it was discovered by UK backpackers and its virtues extolled on the Internet. It was popular in Europe before it was popular in the States.
Just because someone has done a big trip does not mean they are savvy about all the gear that is available in the world. If the gear that you use works reliably then what need is there for gear that is produced elsewhere, that tends to be more expensive, often the language is impossible to read, and you have no idea about its reliability? The tunnel tent with inner clipped in afterwards was first designed in Europe because of the substantial rain in Europe and the desire to get out of that rain quickly without getting everything wet. This type of design has now been set in the minds of Europeans and no one thinks of it as an odd design. But the thinking still hasn't been set in the minds of Americans (or Japanese), so, because they still think in terms of the inner-first, outer-afterwards paradigm, they will often dismiss the tunnel. When the Akto first came to Japan I was talking to a sales clerk at one of the big outdoor stores here, who told me not to consider it because it didn't have a bathtub floor (he assumed that since the fly was pitched first it ought to have a floor... he didn't understand the design). One of the big obstacles when someone designs something... anything... is conceptual blocks; you think in one way and it is very hard to think in a new way. One of Henry Shire's amazing abilities, and quite rare, is his ability to think outside the box. That's why he keeps coming up with so many unique designs. Very few designers can do this.
Changing the minds of consumers is even more difficult. If you introduce something totally new you take a big gamble that the consumers are going to be able to recognize the value of that new thing. There are plenty of examples of designs that were revolutionary, but completely failed in the market, not because they didn't work, but because they were simply overlooked, or they didn't have enough time financially to be refined.
So, unless people like Skurka, Robinson, Jordan, and Tapon (who I'm sure now is very much up on European outdoor gear designs) actively seek out designs outside the States, they are not likely to know them. And certainly not the designs that come out in places like Japan, New Zealand, China, or Czech, all places where outdoor designs are very popular and innovative.