Year-round, we can buy nearly any kind of nut roasted, salted, or dried in markets. You can even get them in convenience stores. For reasons I'm not sure of, chestnuts have never taken off in America the way they have in Asia. This may have something to do with the fact that they can't be gobbled down by the handful with beverage and are a bit moist and often vacuum packed. This doesn't explain why they haven't penetrated American cuisine as deeply as they have Japanese (and I know what you're all thinking after reading that because I know you all have minds that are nearly as filthy as mine).
Chestnuts are a very healthy, relatively low calorie nut. They're creamy and similar to sweet potatoes in texture. So, why aren't we eating more of them? Well, this article in Serious Eats speculates that they fell out of favor when trees started dying due to blight. That writer believes that they were forgotten and never made their way back into people's regular diets. Personally, I think that people are too lazy to do what it takes to make dishes with them (and they aren't great just by themselves as they can be slightly bitter) and too conservative in their eating habits by and large for them to be popular.
All of this is my lamenting that chestnut, or "marron" as they're called in Japan and France, and chestnut-flavored items are so rare here. When I saw this new tea by Karel Capek, I wished very much to be able to get my hands on it. Unfortunately, even if I still lived in Japan, it would require some effort as I'd have to go to Musashino to visit their store (not a small hike from where I used to live) or do mail order. Chances are, appealing as this tea sounds, I wouldn't have troubled myself to do either. I guess that also speaks to why chestnuts aren't more popular. If even someone who loves them as much as I do can't be bothered to make some efforts to get goods made with them, then they probably aren't going to sell especially well.