I considered that viewpoint too, but if you're going to share your game with people who aren't able to go to these events, that's the best way to do it. Also, the same circle sells their games in doujin shops, and I don't see how DLsite, a website specializing in selling doujin comics and games, is any different.
It has to do with the fact that ZUN doesn't want circles to distribute their games too extensively. If they stick to just selling hard copies through either Comiket or places like Toranoana, they can limit how much stock goes on sale, but if they digitally sell online, then their stock becomes limitless and they can't control the extent of their distribution.
I'm not exactly sure why, it might just be that they want to be seen as nothing more than a small collaboration of indie groups, or it might even be that they don't want doujin artists competing with each other for "sales", but I noticed that Touhou doujin community seems to have this mentality that an extensive distribution of their games automatically equals commercialization.
I never agreed with it myself. In fact, I'd say ZUN is shooting himself in the foot by not selling his games on DLsite. I don't think circles who complain about piracy don't have a good reason to do so if they don't even bother selling their games as much as they can, either. The whole purpose of copyright is to protect sales--Why worry about losing sales to piracy if you're not going to make an effort to sell your stuff?
Anyways, it's nice to know that the translation is going smoothly.