@vs3, I'm not much of an analog guy, but isn't it difficult for a QFN package to evenly distribute 50 watts of clean power?  I was under the impression that BGA style packages are used for A) large pin counts, and B) power distribution.  Point B being salient here.  BGAs allow you to get caps closer to the die.  And with designs like mining chips, power distribution is key.

Again, I'm not an analog guy.  I suppose BlackArrow could chime in here, but honestly I think they have more important things on their mind.  Time to market is so much more important than getting the cost of PCB and assembly down.