With how much it cost to release a patch to block flashcards, it's not worth it in the long run since no one who owns a flashcard will go out and buy DS games.
Actually I know a couple others who have flashcarts yet still go out and buy games. About the only games they download are older ones that are either not in stock around where they live or ones that they'd have to get secondhand anyway. Brand new games are a different matter because they like supporting devs. Over time they may download it but by then they usually have played the physical copy at least once or twice and have long since gotten rid of it.
I buy "3DS" games and at one point half of game library I owed or can't find in the stores around me (lost my DS Lite way back). But this doesn't change the fact that they, like me, are not "actively" buying games.
I didn't say anything about 'actively' buying games as there are many people, with or without flashcarts, who don't actively buy games. I was more referring to your statement that having a flashcart(and thus being able to get DS games free) would mean that said owners wouldn't still go out and buy games. I was saying that I still know people who go out/have gone out and buy/bought DS games despite having flashcarts.
Edit: Cut out a lot of the extra quotes.