How Do Bad Units Happen?

I was talking with a buddy of mine and he raised this question - how do bad units happen? Where is the breakdown that causes even otherwise excellent companies to put out the occasional stinker, or screw up an entire faction, or any of the other banes that plague our existences as wargamers?

Personally, I always thought it came down to...
• Someone at the company doesn't know how the game works.
• A bad idea doesn't get caught in time because of a breakdown in playtesting/development.
• A bad idea doesn't get caught in time because of a company culture issue (ie. it's someone powerful's idea).
• There is a breakdown in communication between the company and the consumer (ie. the company doesn't know something is bad, doesn't get how the game is played, doesn't want to deliver something the players want).

But I'm curious to read everyone else's thoughts on the matter.

Designed obsolescence. Intentionally taking something good and "nerfing" it to the point where it's not good for some time, negating the fact that many people spent lots of money on it, and then cycling it back in after they've already bought the new stuff once more.

That doesn't explain units that are just bad from the start, though. Say, the Nephilim.

True. I was just throwing out the big conspiracy theory reason. :-)