I can't say I was front and center to everything happening, but I always thought it was strange that Linux used Bitkeeper which is very not open-source. So many battles have been fought around Linux and GPL that this seemed a bit hypocrtical.

Of course things were run afoul when Tridge started reverse engineering the bk protocol/datastructure but frankly the need to switch away from bk was a bit self-inflicted from what I could tell.