None of that really explains those people who do cycle, and cycle a lot, and 'choose' a 'non-transport' bike though. Because, yes, there aren't many high street sellers of such bikes, or if they are selling the choice isn't massive, but that doesn't mean they're impossible to get hold of.
Is it fashion? Possibly partly. Cross bikes have become popular, but one reason is because they are a bit faster than a mountain bike, but made more sturdy than a road bike, with the ability to put wider tyres on, and if you want to add mudguards, and they're also a more comfortable position than a true 'road' bike, so they can turn very easily into 'transport'.
My Kaff that I commute on I added guards to and a rack, but if it was in a shop window, guardless and rackless, it would be seen as a sportive bike, or cross, or the like. SO also, what is in the window is not necessarily what the bike can become, and many people will be a guardless bike because they like that particular bike, and then add the transport extras.
Basically, what I'm trying to say is that we can choose to see heavier, sturdier, Dutch-style bikes as 'transport' that shows a place has a cycling culture; but in reality any bike whatsoever can be, and is, transport. I don't want a Dutch bike personally, does that mean I don't use a bike for transport, or have become a victim of 'fashion'? No, it just means I've got bikes that suit me and suit my purposes (the Kaff especially has been an evolution to that point).
No matter what you ride etc etc...
On the OP I'm not sure I agree with the article. I think suggesting a lack of access to 'transport' bikes as being a barrier to everyday biking is very very like the line that people not dressed in normal clothes for cycling are a barrier to everyday cycling. I think 'trasnport' bikes of that kind are a consequence of cycling culture, rather than a creator of it (much like the clothing, if cycling is more popular people feel more comfortable). Which I think Crowriver summed up much better than my waffle when saying:
"Until cars become less fashionable/indispensible* then this will not change any time soon.
* - This has happened in central London, due to congestion charging creating quieter streets for cycling/walking and a viable public transport network."