Wow, I was reading up some more on this, with the lawsuit Mattel has pulled against MGA right now, it looks like Bratz may end up in Mattel's hands if they win this intellectual property trial (they claim the Bratz designer, who originally came from Mattel, designed Bratz while still working there, and thus the Bratz line belongs to Mattel). If so, MGA may be finished. If the jury rules in favor of MGA, they can counter-sue Mattel for making their Barbie dolls look more "Bratzy."
Regardless of whose right, I think Mattel is just trying to be a bully, as they have apparently sued everyone who has entered the fashion doll industry. Apparently, when Bratz were becoming hugely popular and they were unaware of a possible intellectual property infringement, they sent a cease-and-desist letter to MGA over a Bratz website they'd made.
Now I have no problem with a big corporation rightfully defending what's theirs, even if they are jerks or not, but I mean even if Mattel is completely in the wrong and knows it, it seems they still would be trying to pull some kind of legal action.
Barbie is their biggest brand, and Bratz knocked Barbie off her perch, so they consider Bratz a monster threat right now.