They provide camoflauge. If homebrew did not exist, such products could be uncontroversially classified as piracy tools, allowing Nintendo to aggressively remove them from the market. Instead they are in a bittorrent-like situation where even though the vast majority of the use is for copyright infringing activity, there is a loud minority that use it for something legal, and all the pirates pretend to be in that minority when accused of breaking the law.

This culture of "homebrew" truly blossomed during the DS era with a huge number of commercially produced rewriteable cartridges, and 3DS piracy is largely a continuation of that.