Why you may ask

The London High Court has ruled that the R4 cartridge for the Nintendo DS is illegal in the U.K.

The ruling against Playables Ltd. is another victory for Nintendo, which has moved aggressively against importers and sellers of the R4 cartridge. Despite the fact that the device enables the use of legal "homebrew" applications, the court sided with Nintendo because the cartridge must bypass the security measures built into the DS in order to work, which is against the law.

"In the UK alone, there have been over 100,000 game copying devices seized since 2009," Nintendo said in a statement. "Nintendo initiates these actions not only on its own behalf, but also on behalf of over 1,400 video game development companies that depend on legitimate sales of games for their survival."

If that last bit sounds familiar, it's because it's very close to a statement the company released following a similar victory against 11 retailers in the Netherlands who were convicted of selling R4 cartridges last week. Earlier in the year, the company won a lawsuit against an R4 seller in Australia and also claimed "20 successful prosecutions" of people selling circumvention devices in Germany.

But as MCV notes, Nintendo's string of victories against the R4 could run up against yesterday's decision by the U.S. government that removing restrictions on mobile devices in order to run unapproved software is not unlawful. That decision has been most commonly referenced in the context of "jailbreaking" iPhones but presumably could also be applied to mobile gaming devices like the DS.
TLDR
Its the law

If I see any more threads about them I will be swinging in mah banhammer