Most likely they'd have to pay royalties to use Bluetooth software on their device, and they deemed the cost too high. The same thing is true for HDMI and other things. They're proprietary, so sometimes devices won't support it so they don't have to pay royalties. (Unrelated, but I honestly don't understand how HDMI still exists though with DisplayPort being available without the licensing costs. It just controls so much of the market that it can't die.)