And simple greed.  Make as much as you can as quickly as you can.  You cant really blame them.  They are fighting tooth and nail with other ASIC/rig makers.  Its not like they have been in business for a hundred years or looking to go another hundred.  The root of the problem is bitcoin core development failed to evolve and keep it P2P and the consequences will be centralization and open the doors to the many downfalls that p2p decentralization solves.

Those who argue that we are not headed to increased centralization sound more and more like denialist.
http://en.wikipedia.org/wiki/Denialism